i 


Main  Lib. 
•  Agric  Dept. 


, 


PRINCIPLES  AND  PRACTICE 
OF  MILK  HYGIENE 


BY 

LOUIS  A.  KLEIN,  V.M.D. 

PKOFEBSOR   OF    PHARMACOLOGY    AND  VETERINARY    HYGIENE    IN   THE  SCHOOL  OF  VETERINARY 
MEDICINE    AT  THE   UNIVERSITY   OF   PENNSYLVANIA,   AND  DEAN  OF  THE  FACULTY 


41  ILLUSTRATIONS  IN  THE  TEXT 


PHILADELPHIA  AND  LONDON 
J.  B.  LIPPINCOTT  COMPANY 


K5 


COPYRIGHT,   1917,   BY  JT.   B.  LIPPINCOTT  COMPANY 


^ttAyVNA^^u) 


FEINTED  BT  J.  B.   LIPPINCOTT  COMPANT 

AT  THE  WASHINGTON  SQUARE  PRESS 
PHILADELPHIA,  TJ.  3.  A. 


*>'  '•  •'•••;• 


PREFACE 

IN  this  book  an  effort  has  been  made  to  present 
systematically,  in  concise  form,  the  facts  and  principles 
which  are  of  importance  in  the  practice  of  milk  hygiene 
and  to  describe  how  they  may  be  applied  in  the  inspec- 
tion of  dairy  farms  and  in  the  examination  of  milk.  The 
material  has  been  obtained  from  various  sources.  Jen- 
sen's "  Milk  Hygiene/'  Savage's  "  Milk  and  the  Public 
Health,"  Conn's  "  Practical  Dairy  Bacteriology,"  Swith- 
inbank  and  Newman's  "  Bacteriology  of  Milk,"  King's 
"  Ventilation,"  Van  Slyke's  "  Modern  Methods  of  Test- 
ing Milk  and  Milk  Products,"  Grimmer's  "  Chemie  und 
Physiologic  der  Milch,"  Rievel's  "  Milchkunde,"  Weig^ 
mann's  "  Mykologie  der  Milch,"  Ernst's  "  Milchhygiene 
fiir  Tierarzte,"  Sommerfeld's  "  Handbuch  der  Milch- 
kunde," and  Barthel's  "  Methoden  zur  Untersuchung 
von  Milch  und  Molkereiprodukten  "  have  been  freely 
drawn  upon,  while  articles  by  numerous  research  workers 
which  have  appeared  in  the  various  journals  and  official 
reports  have  furnished  many  important  facts.  To  all  of 
these  authors  and  investigators  due  acknowledgment  is 
made. 

The  book  is  intended  primarily  as  a  text  for  students 
taking  a  course  in  milk  hygiene,  but  it  is  the  hope  of  the 
author  that  it  will  also  prove  of  service  to  dairy  inspec- 
tors, milk  examiners,  public  health  officials,  dairymen, 
milk  distributers,  and  others  interested  in  the  production 
of  wholesome  milk. 

Louis  A.  KLEIN 

PHILADELPHIA,  PA. 

SEPTEMBER  15,  1917. 


369211 


CONTENTS 

CHAPTER  pAGE 

I.  PHYSIOLOGY  OF  MILK  SECRETION 1 

Udder  Structure  and  Cell  Activity.  Stages  of 
Lactation.  Phases  of  Milk  Secretion. 

II.  COLOSTRUM , U 

Physical  Properties;  Chemical  Properties;  Micro- 
scopic Appearance;  Ferments  or  Enzymes;  Change 
from  Colostrum  to  Milk;  Judgment  of  Colostrum 
as  a  Food  for  Man. 

III.  MILK 14 

Chemical  Properties:  Constituents;  Variations  in 
Composition;  Reaction.  Physical  Properties: 
Color;  Odor  and  Taste;  Specific  Gravity;  Refrac- 
tion; Viscosity;  Freezing  Point.  Microscopical 
Appearance  of  Milk  and  Milk  Sediment:  Cellular 
Content;  Number  of  Cells.  Biological  Properties 
of  Milk:  Ferments  or  Enzymes;  Original  and 
Bacterial  Ferments;  Diastase;  Peroxydase;  Cata- 
lase;  Reductase;  Antibodies  or  Immune  Bodies; 
Germicidal  Action  of  Milk;  Toxins;  Aggressins. 
Classes  or  Grades  of  Market  Milk:  Certified  Milk; 
Inspected  Milk;  Pasteurized  Milk;  Grade  A;  Grade 
B;  Grade  C. 

IV.  BACTERIA  IN  MILK 50 

Common  Milk  Bacteria:  Acid-forming  Bacteria; 
Gas-forming  Bacteria;  Peptonizing  or  Casease 
Bacteria;  Alkali-forming  Bacteria;  Inert  Bacteria. 
Variations  in  Number  and  Kind  of  Bacteria: 
Original  Contamination;  Temperature;  Age  of 
Milk;  Proportion  of  Different  Groups  of  Bacteria. 

V.  MILK  DEFECTS 66 

Milk  Defects  Which  are  Present  in  Milk  when  it 
Comes  from  the  Udder:  Cow-like, or  Salty,  Cow- 
like  Taste;  "Fishy"  Milk;  Rancid  Milk;  Slow- 
creaming  Milk;  Premature  Curdling;  "Gritty"  or 
"  Sandy  "  Milk.  Milk  Defects  which  Appear  After 
the  Milk  is  Drawn  from  the  Udder:  Bitter  Milk; 
Viscid,  "Ropy,"  or  "Stringy"  Milk;  "Soapy" 
Taste;  Failure  to  Sour  and  "Butter;"  Stable-like, 


vi  CONTENTS 

Turnip -like  and  Beet-like  Tastes,  and  a  Burnt  or 
Malt-like  Taste  and  Odor;  Blue  Milk;  Red  Milk; 
Yellow-  or  Orange-colored  Spots;  Yellowish-green 
Discoloration;  Greenish- Yellow  Spots;  Violet- 
colored  Spots. 

VI.  INFLUENCE  OF  DISEASE  UPON  MILK 72 

Diseases  of  Cattle  Transmissible  Through  Milk: 
Tuberculosis;  Aphthous  Fever  or  Foot  and  Mouth 
Disease;  Cow-pox;  False  Cow  Pox;  Furunculosis  of 
the  Udder;  Anthrax;  Rabies;  Actinomycosis;  Milk 
Sickness  or  Trembles.  Diseases  of  Cattle  which 
may  Render  Milk  Harmful  to  Man :  Inflammation 
of  the  Udder  (Mastitis);  Blood  in  Milk;  (Edema 
of  the  Udder;  Indigestion;  Spoiled  Feed;  Septic  or 
Hemorrhagic  Enteritis;  Septic  Metritis;  Retained 
Placenta;  Infectious  Abortion;  Other  Diseases; 
Excretion  of  Medicines  Through  the  Udder. 
Diseases  of  Man  Transmissible  Through  Milk: 
Typhoid  Fever;  Paratyphoid  Fever;  Diphtheria; 
Septic  Sore  Throat;  Scarlet  Fever;  Tuberculosis. 

VII.  DAIRY  FARM  INSPECTION 126 

Stable:  Exterior;  Interior.  Cows:  Examination 
for  Cleanliness;  Stage  of  Lactation;  Examination 
for  Symptoms  of  Diseases.  Stable  Practices: 
Method  of  Cleaning  the  Stable;  Cleaning  the  Cows; 
Methods  of  Milking;  Feeding;  Bedding.  Milk 
House:  Location;  Construction;  Apparatus;  Water 
Supply.  Score  Cards. 

VIII.  PASTEURIZATION 203 

Principles  of  Pasteurization:  Effect  of  Heat  on 
Pathogenic  Organisms;  Effect  of  Heat  on  the 
Common  Milk  Bacteria;  Toxins  and  Decomposi- 
tion Products;  Nutritive  Properties;  Ferments  or 
Enzymes;  Taste;  Cream  Line.  Methods  of  Pas- 
teurization: "Flash"  or  Continuous  Process; 
"Holder"  Process;  Pasteurization  in  the  Final 
Container;  Types  of  Pasteurizers;  Biorization; 
Ultra-violet  Rays;  Electricity;  Ozone. 

IX.  METHODS  OF  EXAMINING  MILK 223 

Collecting  Samples;  Preserving  Samples;  Stable  or 
Herd  Samples;  Individual  Samples;  Mixing  the 
Milk  Sample;  Color,  Consistency;  Odor  and  Taste. 
Determination  of  Specific  Gravity;  Determination 
of  the  Per  Cent,  of  Fat;  Determination  of  Total 


CONTENTS  vii 

Solids;  Determination  of  Solids  Not  Fat;  Deter- 
mination of  the  Specific  Gravity  of  the  Solids; 
Determination  of  the  Per  Cent,  of  Fat  in  the  Total 
Solids;  Determination  of  the  Degree  of  Adultera- 
tion; Tests  for  Nitrates  and  Nitrites;  Detection  of 
the  Usual  Adulterations;  Determination  of  the  Re- 
fraction Number;  Determination  of  the  Reaction; 
Tests  for  Preservatives;  Standard  Methods  of 
Counting  Bacteria;  Examination  for  Streptococci; 
Examination  for  Coli;  Examination  for  Tubercle 
Bacilli;  Fermentation  Test;  Estimation  of  the 
Number  of  Leucocytes;  Boiling  Test;  Alcohol 
Test;  Catalase  Test;  Reductase  Test;  Fermentation 
Reductase  Test;  Diastase  Test;  Tests  for  Heated 
Milk;  Examination  for  Dirt;  Test  for  Lactose;  Ex- 
amination for  Coloring  Matters. 

APPENDIX 303 

Methods  and  Standards  for  the  Production  and 
Distribution  of  "Certified  Milk":  Organization 
of  Medical  Milk  Commissions;  Hygiene  of  the 
Dairy;  Transportation;  Veterinary  Supervision  of 
the  Herd;  Bacteriological  Standards;  Chemical 
Standards  and  Methods;  Methods  and  Regula- 
tions for  the  Medical  Examination  of  Employees, 
Their  Health  and  Personal  Hygiene, 


ILLUSTRATIONS 

FIG.  HALFTONES  PAGE 

1.  Alveoli  of  the  Udder  in  Cross-section g 

2.  Cross-section  of  an  Alveolus  of  the  Udder  at  the  Time 

of  Parturition g 

3.  Involution  of  the  Udder  of  an  Old  Cow 3 

4.  Extremity  of  the  Milk  Cistern 3 

7.  Colonies  of  Coli  Aerogenes 54 

8.  Colonies  of  Proteus  Vulgaris 54 

21.  Internal  or  Double-tube  Cooler 186 

41.  Various  Types  of  Dirt  Testers 300 

TEXT  CUTS 

5.  Preparation  Showing  Streptococcus  Lacticus  or  Bacterium 

Lactis  Acidi 53 

6.  Preparation  from  Sediment  from  a  Cow  Affected  with 

Catarrhal  Mastitis 53 

9.  Inlet  in  a  Wall  Already  Constructed;  Inlet  in  a  Wall 

Being  Built,  and  an  Outlet  Shaft  with  Two  Openings.  .   132 

10.  An  Outlet  Flue  Hinged  at  the  Ceiling 134 

11.  Cross-section  of  Stable  Floor 142 

12.  Window  Arranged  to  Act  as  Fresh  Air  Inlet 147 

13.  Open  or  Uncovered  Pail 171 

14.  Covered-top  Pail  with  Opening  Nearly  Horizontal 171 

15.  Covered-top  Pail  with  Vertical  Opening 172 

16.  Another  Variety  of  Covered-top  Pail 173 

17.  Floor  Plan  of  Conveniently  Arranged  Milk  House 181 

18.  Cooler  of  Conical  Type 183 

19.  Corrugated  Type  of  Cooler 184 

20.  Tubular  Cooler,  with  Continuous  Surface 185 

22.  Section  Showing  Relation  of  Water  Table  to  Surface  Irreg- 

ularities    194 

23.  How  Springs  May  be  Polluted  by  Subsurface  Drainage. .   195 

24.  A  Pasteurizer  of  Simple  Type 216 

25.  Pasteurizer 

fat 


ILLUSTRATIONS 


26.  Pasteurizer , 

27.  Regenerative  Cooler 

28.  A  Simple  Holding  Tank 

29.  Retarder  of  the  Tank  Type 

30.  A  Combined  Pasteurizer  and  Holder , 

31.  Quevenne's  Lactometer 

32.  Westphal  Balance 

33.  Modern  Type  of  Babcock  Milk-testing  Bottle 

34.  Pipette  Used  in  Babcock  Test  for  Measuring  Milk . . 

35.  Cylinder  Used  in  Babcock  Test  for  Measuring  Acid 

36.  Bottle  and  Pipettes  Used  in  Gerber  Test 

37.  Feser's  Lactoscope 

38.  Zeiss  Dipping  Refractometer 

39.  Sediment  Tube  Used  in  the  Trommsdorff  Test 

40.  Gerber-Lobeck  Catalase  Apparatus 


PRINCIPLES  AND    PRACTICE 
OF  MILK  HYGIENE 

CHAPTER  I 

PHYSIOLOGY  OF  MILK  SECRETION 

CERTAIN  facts  concerning  the  physiology  of  milk 
secretion  are  of  importance  in  milk  hygiene.  These  will, 
therefore,  be  briefly  presented. 

Udder  Structure  and  Cell  Activity* — The  udder  or 
mammary  gland  of  the  cow  consists  of  a  large  number 
of  alveoli  or  acini  arranged  in  lobules  or  groups  and 
held  together  by  connective  tissue.  The  alveoli  of  each 
lobule  communicate  with  a  common  duct  which,  after 
emerging  from  the  lobule,  continues  its  course  in  the 
interlobular  connective  tissue  toward  the  milk  cistern. 
The  ducts  from  the  several  lobules  unite  to  form  the 
larger  milk  canals.  The  latter  increase  in  size  as  they 
approach  the  milk  cistern,  in  which  they  terminate. 
From  the  bottom  of  the  milk  cistern,  a  short,  narrow 
canal,  called  the  teat  canal,  extends  through  the  lower 
end  of  the  teat  to  the  exterior.  The  udder  of  the  cow 
contains  four  of  these  glandular  systems,  one  for  each 
teat.  Each  glandular  system  is  spoken  of  as  a  "  quarter." 

The  alveoli  are  lined  with  glandular  epithelial  cells 
which,  in  the  actively  secreting  udder,  are  separated  from 
the  capillaries  by  only  a  thin  basement  membrane.  These 
cells  select  from  the  blood  circulating  in  the  capillaries 
certain  materials  which  they  convert  into  those  substances 


£  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

which  are  peculiar  to  milk.  They  also  take  from  th 
blood,  water  and  other  substances  which  are  commo 
to  milk  and  blood.  In  histological  sections,  the  milk  fa 
may  be  observed  within  the  actively  secreting  cells  i 
the  form  of  small  fat  droplets  ( Fig.  1 ) .  The  other  cor 
stituents  of  milk,  being  without  form,  cannot  be  seer 
but  their  presence  in  the  cells  is  indicated  by  a  granula 
or  turbid  condition  of  the  protoplasm.  When  the  cell 
of  an  alveolus  become  filled  with  secretion,  the  cell-prc 
toplasm  contracts  and  the  contents  is  discharged  into  th 
lumen  of  the  alveolus,  after  which  secretion  again  begin 
The  different  stages  of  cell  activity  do  not  occur  in  all  c 
the  alveoli  at  the  same  time;  different  alveoli  in  the  sam 
lobule  may  show  various  stages.  Secretion  continue 
until  the  cells  are  exhausted,  and  it  then  ceases  unt 
the  cells  can  recuperate. 

In  the  course  of  time,  after  repeated  periods  of  actii 
ity,  exhaustion  and  rest,  the  epithelial  cells  of  the  alveo 
are  worn  out  and  secretion  stops  in  one  alveolus  aft* 
another.  This  change  is  called  involution.  In  youn 
cows  the  worn-out  cells  are  regenerated.  The  alveo 
then  present  the  same  appearance  microscopically  i 
is  observed  at  the  time  of  parturition  (see  Fig.  2) .  Tl 
interalveolar  connective  tissue  is  increased  in  volume  an 
contains  many  leucocytes.  Leucocytes  are  also  numei 
ous  in  the  alveoli,  together  with  exfoliated  epithelii 
cells,  free  nuclei,  parts  of  disintegrated  cells,  fat  globule 
and  coagulated  casein.  Fat  droplets  may  be  observe 
within  some  of  the  leucocytes.  By  their  amoeboid  movi 
ment  the  leucocytes  migrate  from  the  interalveolar  coi 
nective  tissue  into  the  interior  of  the  alveoli,  passin 
between  the  epithelial  cells;  and  the  same  movemei 
enables  them  to  take  up  fat  droplets  and  carry  the] 


FIG.  1. — Alveoli  of  the  udder  in  cross-section,  showing:  (,4)  fat-droplets  in  thp  epithelial 
cells,  (B)  division  of  the  nucleus,  (C)  a  leucocyte  in  an  epithelial  cell,  CD)  epithelial  cell  with 
protoplasmic  projection,  alveolar  content  with  (E)  cells  and  (F)  free  fat,  and  (G)  interalve- 
olar  connective  tissue.  (From  Chemie  und  Physiologic  der  Milch,  by  Dr.  W.  Grimmer.) 


FIG.  2. — Cross-section  of  an  alveolus  of  the  udder  at  the  time  of  parturition.  M) 
epithelium,  (B)  basket  cells,  (C)  leucocytes,  (Z>)  nuclei  of  connective-tissue  cells,  (£)  blood 
capillary.  (From  Chemie  und  Physiologic  der  Milch,  by  Dr.  W.  Grimmer.) 


B 


FIG.  3. — Involution  of  the  udder  of  an  old  cow.  (A)  epithelium,  (B)  leucocytes,  (C) 
blood  capillary,  (D)  interalveolar  connective  tissue.  (From  Chemie  und  Physiologic  der 
Milch,  by  Dr.  W.  Grimmer.) 


FIG.  4. — (^1)  Funnel-shaped,  (B)  bell-shaped  extremity  of  the  milk  cistern.   (From  Chemie 
und  Physiologic  der  Milch,  by  Dr.  W.  Grimmer.) 


PHYSIOLOGY  OF  MILK  SECRETION  3 

out  of  the  alveoli.  An  alveolus  which  has  undergone 
involution  and  regeneration  remains  inactive  until  the 
next  parturition.  As  the  period  of  the  secretory  activity 
of  the  udder  advances,  the  number  of  alveoli  in  this  con- 
dition increase  and  the  quantity  of  milk  secreted  con- 
sequently decreases.  This  change  occurs  slowly  in  some 
cows  and  rapidly  in  others,  and  is  commonly  spoken  of 
as  "going  dry."  Usually  the  secretion  decreases  until 
it  stops  altogether;  the  cow  is  then  said  to  be  "dry."  As 
the  termination  of  secretory  activity  in  the  udder  ap- 
proaches, the  composition  of  the  milk  is  considerably 
changed.  Secretion  of  milk  is  also  called  "lactation," 
and  the  period  during  which  a  cow  produces  milk  is 
called  "a  lactation  period." 

As  the  cow  advances  in  age,  usually  beginning  with 
the  fifth  lactation,  some  of  the  worn-out  alveoli  are  not 
regenerated.  With  each  succeeding  lactation  an  increas- 
ing number  remain  permanently  inactive  or  break  down, 
and  the  quantity  of  milk  produced  is  consequently  de- 
creased. The  interalveolar  and  interlobular  connective 
tissue  gradually  increases  in  volume,  while  the  gland  tis- 
sue decreases.  ( See  Fig.  3. )  Finally  the  udder  becomes 
firm  and  hard  and  is  said  to  be  "fleshy."  A  similar 
change  is  sometimes  caused  by  disease  in  young  as  well 
as  in  old  cows. 

Stages  of  Lactation. — The  function  of  milk  secre- 
tion is  intimately  related  to  the  function  of  reproduction. 
Pregnancy  stimulates  the  development  of  the  gland  tis- 
sue of  the  udder  and  secretion  begins  a  few  days  before 
or  at  the  time  of  parturition.  Why  the  udder  begins 
to  secrete  at  this  time  is  not  known.  Of  the  many  the- 
ories advanced,  that  of  Schein  appears  to  be  the  most 
plausible.  According  to  this  theory,  the  blood  of  the 


4  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

pregnant  cow  contains  certain  substances  called  "milk- 
forming  substances."  During  pregnancy  the  greater 
portion  of  these  substances  is  required  for  the  nourish- 
ment and  development  of  the  foetus,  but  sufficient  is 
left  over  to  stimulate  the  development  of  the  glandular 
tissue  in  the  udder.  When  the  foetus  is  developed,  all 
are  available  for  action  upon  the  udder  and  secretion  is 
stimulated. 

At  the  time  of  parturition  the  udder  does  not  secrete 
milk,  but  a  substance  called  colostrum.  The  alveoli  at 
this  period  contain  many  cells,  entire  and  disintegrated, 
and  leucocytes  are  also  numerous  in  the  interalveolar 
connective  tissue.  The  secretion  is  therefore  rich  in  cells. 
It  also  contains  comparatively  large,  round  bodies  which 
have  the  appearance  of  masses  of  fat  grobules.  These 
are  the  so-called  colostrum  corpuscles,  which  are  re- 
garded by  some  as  leucocytes  which  have  taken  up  a  large 
number  of  fat  globules,  and  by  others  as  exfoliated  epi- 
thelial cells  containing  masses  of  fat  globules.  A  cow 
in  this  stage  of  lactation  is  said  to  be  "fresh." 

During  the  first  week  the  secretion  gradually  changes 
to  milk.  The  alveoli  of  the  udder  are  not  all  active  at 
this  time,  but  those  which  are  inactive  and  which  have 
not  undergone  permanent  involution  resume  their  func- 
tion within  the  succeeding  two  or  three  weeks,  when  the 
secretion  of  milk  reaches  its  highest  point.  Usually  by 
the  end  of  the  first  week  the  leucocytes  have  disappeared 
from  the  alveoli  and  interalveolar  tissue  and  very  few 
cells  are  present  in  the  milk.  But  if  milking  is  delayed 
or  is  incomplete  at  any  time,  or  if  stasis  of  milk  occurs 
from  any  cause,  leucocytes  again  invade  the  alveoli  and 
interalveolar  tissue  in  large  numbers  and  become  nume- 
rous in  the  milk.  Their  appearance  under  these  condi- 


PHYSIOLOGY  OF  MILK  SECRETION  5 

tions  seems  to  be  for  the  purpose  of  preventing  stag- 
nation of  milk  in  the  alveoli;  they  take  up  the  fat  glo- 
bules in  the  alveoli  and  carry  them  off  to  the  lymph 
stream  (Czerny).  Leucocytes  and  exfoliated  epithelial 
cells  are  also  present  in  the  milk  in  large  numbers  in  in- 
flammation of  the  udder. 

Under  natural  conditions,  the  secretion  of  milk  con- 
tinues only  until  the  offspring  is  able  to  masticate  and 
digest  solid  food.  But  in  the  highly  specialized  dairy 
cow,  in  which  the  function  of  the  udder  has  been  greatly 
developed,  lactation  may  continue  for  as  long  as  one 
to  two  years  if  reimpregnation  does  not  take  place,  pro- 
vided the  milk  is  regularly  withdrawn.  When  the  cow 
is  reimpregnated,  lactation  usually  ceases  within  a  few 
weeks  of  parturition,  but  in  some  individuals  it  continues 
without  interruption  from  one  parturition  to  the  next. 
In  these  latter  animals,  the  secretion  changes  to  colos- 
trum a  few  days  before  parturition.  Cows  in  which  lac- 
tation is  about  to  cease  are  called  "strippers."  Near  the 
end  of  lactation  the  milk  changes  very  much  in  composi- 
tion and  the  cellular  content  again  increases.  Quite  fre- 
quently it  has  a  salty  or  bitter  taste,  or  an  animal-like 
taste  and  odor  which  are  unpleasant.  It  is  considered 
good  practice  to  give  the  udder  and  the  organs  of  diges- 
tion an  opportunity  to  rest  and  recuperate  before  a  new 
lactation  period  begins,  and  "  persistent  milkers  "  are 
frequently  "dried  off"  about  a  month  before  the  suc- 
ceeding parturition  is  due.  This  can  usually  be  accom- 
plished by  reducing  the  feed  and  gradually  stopping 
milking.  Periodical  emptying  of  the  udder  is  necessary 
for  the  continuance  of  milk  secretion,  and  the  opposite 
effect  is  produced  when  milking  is  incomplete  or  is 
omitted. 


6  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Phases  of  Milk  Secretion. — All  of  the  milk  obtained 
from  the  udder  at  one  milking  is  not  secreted  before 
the  withdrawal  of  the  milk  is  begun.  The  average  vol- 
ume of  the  cavities  of  the  udder  is  3,000  c.c.,  or  about  3 
quarts,  while  the  average  yield  of  milk  at  one  milking 
is  from  4,000  to  6,000  c.c.,  or  about  4  to  6  quarts  (Fleisch- 
mann) .  A  large  part  of  the  milk  obtained  at  a  milk- 
ing is  secreted  while  the  cow  is  being  milked.  As  much 
milk  is  secreted  in  ten  to  fifteen  minutes  during  milking 
as  is  formed  during  the  entire  period  between  milkings. 
The  secretion  of  milk  may  be  divided  into  two  phases 
(Zietzschmann) . 

The  first  phase  occurs  during  the  intervals  between 
milkings.  Following  the  completion  of  a  milking,  the 
gland  remains  at  rest  for  a  short  time  until  the  exhausted 
secretory  cells  can  recuperate ;  then  secretion  is  resumed, 
and  gradually  increases  in  intensity  up  to  a  certain  point. 
The  udder  gradually  becomes  larger  and  firmer,  but  the 
teats  remain  relaxed  and  pendulous  and  contain  only  a 
small  quantity  of  milk.  The  greater  part  of  the  milk 
secreted  during  the  first  phase  remains  in  the  alveoli 
and  the  large  milk  canals.  There  are  two  reasons  for 
this:  (1)  the  horizontal  direction  of  the  large  milk  canals 
does  not  favor  the  flow  of  milk  into  the  cistern,  and  (2) 
the  inward  pressure  of  the  erectile  tissue  in  the  teat  causes 
the  mucous  membrane  to  project  into  the  cistern  in  folds, 
filling  up  the  cavity  and  opposing  the  flow  of  milk  into 
it.  When  the  alveoli  and  the  milk  ducts  and  canals  be- 
come full,  secretion  decreases  in  intensity.  Under  ordi- 
nary conditions  the  pressure  in  the  alveoli,  ducts,  and 
canals  does  not  become  sufficient  to  overcome  the  coun- 
terpressure  exerted  by  the  erectile  tissue  in  the  teats, 


PHYSIOLOGY  OF  MILK  SECRETION  7 

and  consequently  the  milk  cistern  remains  practically 
empty. 

The  second  phase  of  milk  secretion  begins  when  the 
udder  is  stimulated  reflexly  by  manipulation  of  the  teats. 
The  udder  becomes  fuller  and  more  tense,  the  gland  sub- 
stance firmer.  The  teats  lengthen  and  become  rigid 
and  divergent,  while  the  wrinkles  disappear  from  the 
skin  covering  them.  The  udder  is  distended  and  the 
cisterns  are  full  of  milk.  The  milk  has  been  "let  down." 
All  these  changes  are  brought  about  by  the  downward 
stroking  of  the  teats,  which  causes  reflexly  (1)  dilation 
of  the  blood  vessels  and  an  increased  flow  of  blood  to 
the  udder,  (2)  contraction  of  the  walls  of  the  alveoli 
and  ducts,  which  forces  the  milk  down  into  the  cisterns, 
and  (3)  increased  secretion  of  milk.  The  same  effect 
may  be  produced  reflexly  by  an  irritation  of  the  inter- 
nal genital  organs  such  as  may  result  from  irrigation 
of  the  uterus  or  vagina,  or  manual  removal  of  the  pla- 
centa, and  also  by  psychic  influences  like  the  sight  of 
the  calf,  the  clatter  of  the  milk  vessels,  the  sound  of  milk 
drawn  from  another  cow  into  a  pail,  etc.  When  the 
interval  between  milkings  is  too  long  the  milk  is  "let 
down"  spontaneously,  but  in  this  case  it  occurs  grad- 
ually. 

As  soon  as  the  milk  is  sufficiently  "  let  down  "  the 
withdrawal  of  milk  may  be  begun.  The  descending  pres- 
sure exerted  by  the  hand  upon  the  contents  of  the  milk 
cistern  in  the  operation  of  milking  opens  the  sphincter 
between  the  teat  canal  and  the  cistern,  permitting  the 
milk  to  escape.  This  pressure  operates  perpendicularly 
to  the  wall  of  the  cistern,  and  when  the  bottom  of  the 
cistern  is  pointed  or  conical  the  sphincter  is  opened  more 
readily  than  when  the  bottom  is  flat  (see  Fig.  4).  The 


8  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

manipulation  of  the  teats  in  milking  causes  the  hyper- 
asmia  and  increased  secretion  set  up  by  stroking  the  teats 
to  continue  until  the  secreting  cells  are  exhausted,  when 
the  flow  of  milk  ceases  and  the  udder  becomes  smaller 
in  size  and  relaxed.  The  manipulation  of  one  teat  pro- 
duces hypersemia  and  stimulates  secretion  in  all  four 
quarters  of  the  udder.  The  second  phase  of  milk  secre- 
tion is  therefore  due  to  the  mechanical  stimulation  result- 
ing from  the  manipulation  of  the  teats  in  milking.  The 
stimulating  apparatus  is  in  the  teats,  but  it  is  not  clear 
how  the  stimuli  .are  transmitted.  The  udder  is  richly 
supplied  with  nerves  from  the  sympathetic  system  and 
from  the  lumbar  plexus,  and  yet  secretion  can  go  on 
after  the  greater  part  of  the  nerve  apparatus  is  discon- 
nected. 

Three  factors  are  concerned  in  the  second  phase  of 
milk  secretion:  (1)  The  vasodilator  nerves  are  stimu- 
lated reflexly  by  the  mechanical  manipulation  of  the 
teats  in  milking,  producing  a  hypersemia  and  bringing 
a  rich  supply  of  milk-forming  material  to  the  secreting 
cells.  (2)  The  operation  of  milking  stimulates  also  the 
secretory  and  the  motor  nerves ;  stimulation  of  the  secre- 
tory nerves  accelerating  the  secretory  processes  in  the 
cells  of  the  alveoli,  and  stimulation  of  the  motor  nerves 
causing  a  contraction  of  the  alveoli  and  ducts  and  forcing 
the  milk  into  the  cistern.  (3)  The  "  milk-formers,"  which 
circulate  in  the  blood,  stimulate  the  secretory  cells 
(Zietzschmann). 

Under  certain  abnormal  conditions  the  secretion  of 
the  second  phase  stops  before  the  usual  amount  of  milk 
is  obtained.  This  may  result  from  fright,  sudden  anx- 
iety, and  in  sensitive  animals  from  unusual  manipulation 
of  the  teats  (strange  milkers) ,  from  sore  teats,  etc.  The 


PHYSIOLOGY  OF  MILK  SECRETION  9 

distended  udder  is  suddenly  reduced  in  size  and  becomes 
relaxed.  This  is  due  to  a  reflex  contraction  of  the  blood 
vessels,  which  reduces  the  blood  supply,  and  to  the  empty- 
ing of  the  milk  cisterns.  Contraction  of  the  blood-vessels 
slightly  enlarges  the  alveoli  and  ducts,  creating  a  va- 
cuum, and  the  milk  in  the  cisterns  is  drawn  up  into  the 
alveoli  and  ducts.  It  is  then  said  the  cow  "draws  the 
milk  up,"  or  "will  not  give  down."  In  these  cases  the 
physiological  effect  of  the  manipulation  of  the  teats  in 
milking  is  overcome  by  a  stronger  impulse.  If  these 
impulses  are  repeated  frequently,  or  are  due  to  more 
or  less  permanent  conditions,  like  chronic  sores  on  the 
teats,  the  shortening  of  the  second  phase  may  become 
habitual  or  permanent. 

The  secretion  of  the  first  phase  is  passive  and  slow. 
According  to  Zietzschmann,  it  is  due  to  the  stimulant 
effect  upon  the  gland  cells  of  the  "milk- formers"  cir- 
culating in  the  blood. 

The  secretion  of  the  second  phase  is  active  and  rapid, 
and  is  instituted  and  continued  by  the  manipulation  of 
the  teats  in  milking. 

Within  certain  limits,  increasing  the  number  of  milk- 
ings,  thus  shortening  the  period  between  milkings,  will 
increase  the  total  daily  yield  of  milk.  If  milked  three 
times  in  twenty-four  hours,  a  cow  will  usually  yield  a 
greater  total  quantity  of  milk  per  day  than  when  milked 
twice  in  twenty-four  hours. 

The  composition  of  the  milk  is  different  in  the  first 
and  second  phases.  The  first  milk  drawn  from  the  udder 
at  any  milking  will  contain  a  smaller  proportion  of 
solids,  especially  fat,  than  the  succeeding  milk.  This  is 
not  due  to  the  fat  rising  to  the  top  of  the  fluid  in  the 
udder,  nor  to  the  adhesion  of  the  fat  globules  to  the  walls 


10          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

of  the  alveoli  and  ducts,  as  has  been  suggested,  because 
when  milk  is  drawn  from  the  udder  at  the  end  of  the 
first  phase  with  a  milk  tube  or  catheter  the  composition 
of  the  first  and  last  milk  is  about  the  same;  but  as  soon 
as  the  teats  are  manipulated,  thus  beginning  the  second 
phase,  the  per  cent,  of  fat  is  increased.  The  milk  se- 
creted during  the  first  phase  contains  a  lower  per  cent, 
of  fat  than  that  formed  in  the  second  phase.  The  per 
cent,  of  other  solids  is  nearly  the  same  in  the  milk  of 
both  phases.  The  original  ferments  or  enzymes,  except 
oxydase,  are  present  in  greater  quantity  in  milk  of  the 
second  phase  than  in  that  of  the  first.  The  first  milk 
drawn  from  the  udder  contains  more  oxydase  than  the 
end  milk. 


CHAPTER  II 

COLOSTRUM 

Beginning  a  few  days  before  and  continuing  for  sev- 
eral days  after  parturition,  the  udder  secretes  a  substance 
called  "colostrum,"  which  differs  in  many  respects  from 
milk.  This  fluid  is  intended  for  the  nourishment  of  the 
calf  during  the  first  days  of  life  outside  of  the  uterus  of 
the  mother.  It  contains  a  very  high  per  cent,  of  albumi- 
nous compounds  in  a  form  in  which  they  can  be  readily  ab- 
sorbed from  the  digestive  tract  of  the  young  animal.  It 
also  contains  protective  substances  from  the  mother 
(Engel) ,  which  are  of  value  in  maintaining  health  (Im- 
misch),  and  it  has  a  laxative  action  upon  the  bowels  of 
the  calf,  which  results  in  the  removal  of  the  meconium. 

Physical  Properties. — Colostrum  is  of  a  yellowish, 
reddish-yellow,  or  brownish  color;  of  a  thick,  slimy,  sticky 
or  "stringy"  consistency,  with  a  peculiar  unpleasant  odor 
and  a  salty  taste.  The  yellowish  color  is  due  to  the  pres- 
ence of  fat  globules,  which  are  frequently  clumped  to- 
gether, while  the  reddish  or  brownish  tinge  is  due  to 
the  presence  of  red-blood  cells  or  blood.  Containing  a 
much  greater  per  cent,  of  solids  than  milk,  its  specific 
gravity  is  naturally  much  higher,  ranging  from  1.040 
to  1.080  and  even  up  to  1.090. 

Chemical  Properties. — 'Albumin  and  globulin  are 
present  in  colostrum  in  considerably  greater  quantity 
than  in  milk.  Nuclein  compounds  are  also  to  be  found 
in  larger  proportion.  There  is  less  casein  and  sugar, 
about  the  same  per  cent,  of  extractives,  but  a  greater 

proportion  of  mineral  salts.    The  analysis,  as  given  by 

11 


12  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Eugling,  is  as  follows:  Casein  2.65  per  cent.,  albumin 
and  globulin  16.55  per  cent.,  sugar  3  per  cent.,  extrac- 
tives 3.54  per  cent.,  ash  1.18  per  cent.,  and  water  73.07 
per  cent.  The  high  content  of  albumin  and  globulin  is 
due  to  the  presence  of  the  colostrum  bodies  and  nume- 
rous other  cells.  The  sugar  is  not  lactose,  as  in  milk, 
but  glucose,  or  perhaps  a  mixture  of  glucose  and  galac- 
tose  (Tereg).  Of  the  extractives,  about  78.2  per  cent. 
is  fat,  13.8  per  cent,  cholesterin,  and  8  per  cent,  leci- 
thin. The  fat  differs  from  that  of  milk  and  is  apparently 
similar  to  the  fat  of  the  tissues.  The  mineral  salts  are 
rich  in  magnesia,  to  which  is  attributed  the  laxative  ef- 
fect of  colostrum. 

The  reaction  is  acid  to  litmus.  For  two  to  four  days 
after  parturition  the  secretion  coagulates  when  boiled 
(see  boiling  test),  on  account  of  the  large  quantity  of 
albumin  and  globulin  present,  while  it  curdles  for  four 
to  twelve  days  after  parturition  when  mixed  with  an 
equal  volume  of  68  per  -cent,  alcohol  (see  alcohol  test). 

Microscopic  Appearance. — Viewed  under  the  micro- 
scope, colostrum  is  seen  to  contain  free  fat  globules, 
which  are  not  uniform  in  size  like  those  seen  in  milk; 
colostrum  bodies  or  corpuscles,  which  are  comparatively 
large,  round  or  mulberry-shaped  masses,  containing  fat 
globules ;  leucocytes,  some  of  which  contain  fat  globules, 
and,  in  fresh  colostrum,  show  amoeboid  movement;  and 
epithelial  cells,  which  are  more  or  less  disintegrated.  The 
colostrum  bodies  are  cells  which  contain  large  masses  of 
fat  globules  within  their  protoplasm,  but  opinions  differ 
as  to  whether  they  are  leucocytes  or  epithelial  cells. 

Ferments  or  Enzymes. — Catalase  and  diastase  are 
present  in  colostrum  in  greater  amount  than  in  milk,  but 
at  the  end  of  the  first  week  after  parturition  they  are 


COLOSTRUM  13 

reduced  to  the  amount  normally  found  in  milk.  Oxydase 
and  peroxydase  may  be  absent  for  thirty  hours  or  less 
f ollowing  parturition,  but  after  that  time  they  are  usually 
present  (Gruber). 

The  bactericidal  power  of  colostrum  is  greater  than 
that  of  milk. 

Change  from  Colostrum  to  Milk. — The  secretion  of 
the  udder  changes  gradually  in  appearance  and  com- 
position until,  in  about  a  week  after  parturition,  it  be- 
comes milk.  According  to  Weber,  the  consistency  is 
changed  to  that  of  milk  by  the  second  to  the  fifth  day, 
usually  by  the  third;  the  color  by  the  third  to  the  eighth 
day,  usually  by  the  fifth,  and  the  reaction  by  the  seventh 
day,  although  this  is  variable.  The  colostrum  bodies 
persist  for  variable  periods.  In  some  cows  they  continue 
to  be  present  indefinitely  in  small  number,  while  in 
others  they  are  absent  even  in  the  first  days  of  secre- 
tion. Shortly  before  the  lactation  ceases  they  again  be- 
come numerous. 

Judgment  of  Colostrum  as  a  Food  for  Man. — While 
colostrum  is  of  great  value  to  the  new-born  calf,  it  is 
not  considered  desirable  as  human  food.  It  has  not  been 
proven  to  be  injurious  to  the  health  of  man,  but  the 
odor  and  taste  are  obnoxious,  and  its  appearance  is  unap- 
petizing. Regulations  of  local  health  authorities  for 
the  control  of  milk  supplies,  therefore,  forbid  the  sale  of 
the  product  of  a  cow  for  food  purposes  usually  for  one 
week  after  parturition,  and  also  for  fifteen  days  before. 
It  has  been  proposed  by  Weber  that  the  use  of  the  udder 
secretion  be  prohibited  for  general  food  purposes  as  long 
as  it  coagulates  when  boiled  (2  to  4  days),  and  that  its 
use  for  children  be  forbidden  as  long  as  it  continues  to 
react  to  the  alcohol  test  (4  to  12  days). 


CHAPTER  III 

MILK 

The  fluid  known  as  "milk"  consists  of  water  and 
certain  solids.  The  latter  are  in  solution,  in  suspension, 
and  in  emulsion.  In  order  to  comprehend  the  various 
changes  which  may  occur  in  milk  and  to  understand  the 
different  methods  for  its  examination,  it  is  necessary  to 
have  some  knowledge  of  its  physical  and  chemical  prop- 
erties, its  microscopic  appearance,  the  ferments  or 
enzymes  it  contains,  and  the  bacteria  with  which  it  may 
be  contaminated.  These  points  will  therefore  be  given 
consideration. 

CHEMICAL  PROPERTIES 

Constituents. — The  principal  chemical  constituents  are 
casein,  lactalbumin,  lactoglobulin,  fat,  lactose,  mineral 
salts,  and  water. 

Casein  is  a  nucleo-albumin  and  therefore  contains 
phosphorus.  It  is  insoluble  in  water  when  free  and  un- 
combined.  But  in  milk  it  is  combined  with  calcium  in 
the  form  of  dicalcium  caseinate.  This  compound,  which 
is  neutral  to  litmus  and  acid  to  phenolphthalein,  is  re- 
sponsible for  the  white  color  of  milk,  and  in  part  for  its 
opacity.  It  is  not  in  solution  in  milk,  but  in  suspension. 
When  milk  is  exposed  to  a  low  temperature  the  calcium 
caseinate  forms  flakes,  which,  when  the  temperature  is 
sufficiently  low,  are  visible  to  the  eye;  it  is  also  more 
readily  precipitated.  This  must  be  kept  in  mind  when 
the  alcohol  test  is  used  (page  285). 

If  an  acid  is  added  to  milk  the  casein  is  precipitated. 
14 


MILK  15 

The  same  thing  occurs  when  the  lactose  in  the  milk  is 
fermented  by  bacteria  and  a  sufficient  quantity  of  acid 
is  produced.  The  calcium  caseinate  is  split  up.  The 
acid  combines  with  the  calcium,  while  the  free  casein, 
being  insoluble,  is  precipitated  in  the  form  of  a  firm, 
jelly-like  white  curd.  Subsequently  this  curd  contracts 
and  expresses  a  fluid  called  whey,  which  contains  some 
of  the  milk  fat,  the  albumin  and  globulin,  the  milk  sugar, 
the  mineral  salts,  and  the  calcium  salt  formed  by  the 
combination  of  the  acid  with  the  calcium.  Most  of  the 
fat  remains  in  the  curd  with  the  casein.  This  is  the  com- 
mon sour  curdling  of  milk.  If  lime  water  or  a  dilute 
solution  of  an  alkali  is  added,  the  casein  will  be  redis- 
solved  and  the  acidity  reduced. 

Rennet  or  chymosin  also  causes  curdling  of  milk.  In 
this  case  the  calcium  caseinate  is  split  up  by  the  rennet 
into  calcium  paracaseinate  and  a  substance  known  as 
whey-proteid.  Calcium  paracaseinate,  being  insoluble, 
is  precipitated  and  forms  a  curd,  while  the  whey-proteid 
is  held  in  solution  in  the  whey.  Certain  bacteria  produce 
a  rennet-like  ferment,  which  splits  up  the  casein  com- 
pound of  milk  in  the  same  manner.  This  is  the  sweet 
curdling  of  milk,  so  called  because  the  milk  curdles  with- 
out souring.  The  curd  produced  in  this  way  cannot 
be  redissolved  by  lime  water  or  a  dilute  solution  of  an 
alkali.  Curdling  of  milk  may  occur  from  the  joint  action 
of  acids  and  the  rennet-like  ferment.  The  blood  contains 
a  ferment,  called  anti-rennet,  which  inhibits  the  action 
of  rennet.  This  ferment  is  not  present  in  normal  milk, 
but  when  inflammation  occurs  in  the  udder  and  there  is 
a  transudation  of  serum  from  the  blood-vessels  into  the 
udder  tissue  the  anti-rennet  ferment  is  present  in  the 
udder  secretion,  which  is  then  not  coagulated  by  rennet 


16          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

at  all,  or  only  after  several  times  the  usual  amount  of 
rennet  is  added.  A  method  based  upon  these  facts  has 
been  proposed  by  Schern  for  detecting  milk  from  cows 
affected  with  mastitis,  but  the  test  has  not  come  into 
very  general  use,  because  it  has  not  been  found  possible 
to  obtain  a  standardized  rennet  solution  which  will  not 
deteriorate. 

Fresh  milk  may  be  heated  to  boiling  without  coagula- 
tion occurring.  A  thin  membrane,  which  consists  prin- 
cipally of  casein,  forms  on  the  surface,  but  real  coagula- 
tion does  not  take  place.  After  a  certain  degree  of  acid- 
ity has  been  reached  a  temperature  of  75°  C.  (167°  F.) 
is  sufficient  to  coagulate  the  casein. 

Casein  is  formed  by  the  secreting  cells  of  the  alveoli 
of  the  udder  from  the  circulating  albumin  of  the  blood 
(Rievel). 

Lactalbumin.- — The  albumin  of  milk  is  in  solution. 
It  is  similar  to  the  albumin  of  the  blood,  but  differs 
slightly  in  its  chemical  composition  and  polarization. 
It  begins  to  coagulate  at  65.6°  C.  (150°  F.),  and  the 
coagulation  increases  with  the  temperature  (Hupp). 
Whether  the  albumin  originates  from  the  breaking  down 
of  cells  or  is  derived  from  the  blood  is  not  known. 

Lactoglobulin. — The  globulin  of  milk  originates 
from  the  disintegration  of  cells,  and  is  present  in  milk 
in  solution.  It  coagulates  at  75°  C.  ( 167°  F.) . 

Fat. — The  fat  is  present  in  milk  in  an  extremely 
finely  divided  condition — i.e.,  in  an  emulsion.  Under 
the  microscope  it  can  be  observed  in  the  form  of  small 
globules.  The  specific  gravity  of  the  fat  is  lighter  than 
that  of  any  of  the  other  milk  constituents,  including  the 
water,  being  only  0.93.  Consequently  the  fat  globules 
in  milk  are  buoyant,  and  when  the  milk  is  permitted 


MILK  17 

to  stand  undisturbed  they  rise  to  the  top  and  in  a  very 
short  time  form  a  layer  on  the  top  of  the  fluid,  which 
is  known  as  the  cream  layer  or  the  cream  line.  By  many 
consumers  the  quality  of  milk  is  judged  solely  by  the 
thickness  of  the  cream  layer.  When  the  cream  is  re- 
moved the  remaining  fluid  is  called  skim  milk;  or  it  is 
called  separator  milk  when  the  cream  is  removed  by  a 
centrifugal  apparatus  known  as  a  separator. 

The  fat  globules  vary  in  size  with  the  breed,  the  stage 
of  lactation,  the  feed,  at  different  periods  of  the  same 
milking,  and  with  the  individual.  In  the  milk  of  Jersey 
and  Guernsey  cows  the  fat  globules  are  larger  than  they 
are  in  the  milk  of  Holsteins  and  Ayrshires.  The  cream 
rises  more  rapidly  when  the  globules  are  large  than  when 
they  are  small. 

Moderately  high  temperatures  also  favor  the  sepa- 
ration of  the  fat  globules  from  the  remainder  of  the 
milk;  therefore  when  milk  is  to  be  run  through  a  sepa- 
rator it  is  usually  warmed  to  32°  C.  (90°  F.).  On  the 
other  hand,  higher  temperatures  delay  or  entirely  pre- 
vent the  formation  of  a  cream  layer.  Temperatures 
above  70°  C.  (158°  F.)  destroy  the  cream  line  entirely. 
A  temperature  of  65°  C.  (149°  F.)  for  ten  minutes  has 
no  effect,  but  as  the  time  of  exposure  at  this  tempera- 
ture is  increased  the  formation  of  the  cream  layer  is 
delayed  more  and  more,  until  finally,  after  forty  min- 
utes' exposure,  it  does  not  form  at  all.  Milk  may  be 
heated  at  63°  C.  (145.4°  F.)  for  thirty  minutes  and  at 
60°  C.  (140°  F.)  for  as  long  as  fifty  minutes  without 
affecting  the  cream  line.  The  cream  does  not  rise  in 
homogenized  milk  because  the  fat  globules  have  been 
broken  up  into  fine  particles.  Such  milk  is  said  to  be 
more  palatable  and  more  digestible  than  ordinary  milk, 

2 


18  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

but  these  advantages  are  overbalanced  by  the  expense 
of  the  process. 

When  milk  is  shaken  or  agitated  the  fat  globules 
gradually  unite  and  form  flakes  or  lumps — i.e.,  butter. 
Small  clumps  of  butter  fat  may  form  in  milk  during 
transportation  when  the  container  is  not  full.  This 
change  may  affect  the  test  for  fat.  If  milk  or  cream 
is  slightly  acid  and  warm,  the  clumping  of  the  fat  glo- 
bules is  facilitated.  Hence  cream  is  usually  churned 
after  it  has  attained  an  acidity  0.4  per  cent.,  and  at  a 
temperature  of  21°  C.  (70°  F.).  Cream  from  a  cow 
near  the  end  of  lactation  may  not  "butter"  because  of 
its  alkalinity. 

The  fat  of  milk  differs  in  its  chemical  and  physical 
properties  from  both  the  fat  of  the  tissues  and  the  fat 
of  the  food.  It  consists  of  a  mixture  of  fats,  princi- 
pally olein,  stearin,  and  palmatin,  together  with  some 
butyrin  and  other  fats.  Its  composition  varies,  being 
influenced  by  the  breed,  feed,  external  conditions,  etc. 
Cotton-seed  meal,  for  example,  increases  the  olein  and 
raises  the  melting  point.  When  milk  fat  decomposes, 
butyric  acid  is  liberated  and  produces  a  rancid  odor  and 
taste.  The  color  of  the  milk  fat  is  more  or  less  yellow. 
The  fat  globules,  by  reflecting  the  light,  are  partly  re- 
sponsible for  the  opacity  of  milk. 

In  regard  to  the  origin  of  the  milk  fat,  it  appears 
most  probable  that  it  is  derived  in  part  from  the  splitting 
up  of  albuminous  compounds  in  the  udder  or  in  another 
part  of  the  body,  or  in  both  places.  It  may  also  be  formed 
from  the  carbohydrates  which  are  carried  to  the  udder 
by  the  blood  (Rievel). 

Lactose. — This  substance,  also  known  as  "milk 
sugar,"  is  in  solution  in  milk.  It  is  a  disaccharid  and 


MILK  19 

may  undergo  different  varieties  of  fermentation  when 
acted  on  by  microorganisms.  Certain  bacteria  split  up 
lactose  into  lactic  acid  and  certain  by-products  (carbon 
dioxide,  hydrogen,  formic  acid,  butyric  acid,  etc. ) .  These 
organisms  are  the  cause  of  the  common  "souring"  and 
curdling  of  milk.  The  bacteria  of  the  coli-aerogenes 
group  ferment  lactose  and  form  acids  and  gases  (lactic, 
acetic,  and  succinic  acids,  carbon  dioxide,  carburetted 
hydrogen,  oxygen,  and  nitrogen) . 

Under  normal  conditions,  lactose  is  found  only  in 
the  milk.  If  milk  is  retained  in  the  udder  from  any 
cause,  as  incomplete  milking,  omission  of  milking,  udder 
disease,  etc.,  then  lactose  appears  in  the  urine.  When  a 
secreting  udder  is  completely  extirpated,  glucose  is  tem- 
porarily present  in  excess  in  the  blood  and  appears  in 
the  urine,  while  lactose  appears  in  the  urine  if  the  udder 
tissue  is  not  completely  removed.  These  latter  facts  are 
taken  to  indicate  that  milk  sugar  is  formed  in  the  udder 
from  the  glucose  carried  to  it  by  the  'blood. 

Salts. — The  salts  of  milk,  which  are  in  solution,  are 
very  largely  inorganic.  Calcium,  potassium,  and  sodium, 
together  with  small  quantities  of  magnesia  and  oxide 
of  iron,  are  present  in  combination  with  phosphoric  acid, 
sulphuric  acid,  chlorine,  and  carbonic  acid.  A  small  por- 
tion of  the  basic  substances  is  in  combination  with  citric 
acid  and  probably  with  other  organic  acids. 

Water. — The  water  of  milk  is  derived  from  the  blood. 
The  milk  constituents,  except  the  water,  are  referred 
to  as  the  milk  solids,  total  solids,  or  dry  matter.  The 
casein,  albumin,  globulin,  lactose,  and  salts  are  desig- 
nated as  solids  not  fat. 

Variations  in  Composition. — While  normal  milk  always 
contains  the  same  chemical  constituents,  the  proportions 


20          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

in  which  they  are  present  vary  very  much.  The  fat  shows 
a  greater  variation  than  the  other  solids.  In  milk  rich 
in  total  solids,  the  fat  content  is  frequently  considerably 
above  the  average,  while  the  per  cent,  of  solids  not  fat 
only  slightly  exceeds  the  average.  On  the  other  hand, 
in  thin,  poor  milk  the  fat  per  cent,  may  be  far  below 
the  average,  while  the  per  cent,  of  solids  not  fat  is  not 
very  far  from  the  average.  Milk  from  individual  cows 
shows  a  greater  variation  in  composition  than  different 
samples  of  market  milk,  which  is  a  mixture  of  the  milk 
from  a  number  of  cows. 

Individual  milk  may  show  the  following  variations 
in  the  proportion  of  the  different  constituents:  fat,  2.5 
to  7.5  per  cent. ;  lactose,  4  to  5.8  per  cent. ;  casein,  2  to  5 
per  cent.;  albumin,  0.39  to  0.95  per  cent.;  globulin,  a 
trace;  salts,  0.35  to  1.21  per  cent.;  water,  83  to  89  per 
cent. 

The  fat  content  shows  the  greatest  range  of  varia- 
tion and  the  lactose  the  least.  These  variations  must  be 
taken  into  consideration  in  collecting  samples  of  milk 
for  certain  tests  and  in  judging  the  results  of  tests  for 
adulteration  and  skimming.  They  are  due  to  a  number 
of  causes. 

Some  of  these  causes,  such  as  the  breed,  individuality, 
and  stage  of  lactation,  are  more  or  less  regular  and  con- 
stant in  their  operation.  As  a  rule,  cows  of  the  Jersey 
and  Guernsey  breeds  give  milk  richer  in  fat  than  Hoi- 
steins  and  Ayrshires,  but  some  individuals  of  the  Hoi- 
stein  and  Ayrshire  breeds  give  milk  with  a  higher  fat 
content  than  some  Jerseys  and  Guernseys.  Early  in  the 
stage  of  lactation,  when  the  milk  flow  is  most  abundant, 
the  proportion  of  solids,  especially  the  fat,  is  less  than  it 
is  later,  when  the  milk  flow  has  decreased.  Instances 


MILK  21 

are  known  where  the  addition  of  several  "fresh"  cows 
to  a  small  herd  at  the  same  time  has  reduced  the  fat  per 
cent,  of  the  mixed  milk  below  the  standard  formerly 
maintained.  In  the  last  month  of  lactation,  when  the 
secretion  decreases  rapidly,  the  proportion  of  solids 
usually  increases,  especially  the  fat.  At  the  same  time, 
the  secretion  reacts  decidedly  alkaline  to  litmus  paper 
and  usually  has  a  salty  taste;  sometimes  it  has  an  animal- 
like  odor  and  taste.  Cows  in  this  stage  of  lactation  are 
called  "strippers."  In  exceptional  cases  the  milk  does 
not  show  any  noticeable  change  in  chemical  composition 
during  the  entire  period  of  lactation,  while  in  rare  cases 
the  per  cent,  of  solids  may  decrease  at  the  end  of  lacta- 
tion. At  different  stages  of  the  same  milking  the  milk 
also  shows  a  regular  and  constant  variation  in  composi- 
tion, the  first  milk  drawn  containing  a  lower  per  cent, 
of  fat  than  the  last  or  "end"  milk.  Incomplete  milking 
may  lower  the  per  cent,  of  fat,  because  the  end  milk  is 
much  richer  in  fat  than  the  first  milk. 

Transitory  and  irregular  variations  in  composition 
may  be  observed  in  the  milk  of  the  same  cow  from  day 
to  day,  or  even  in  the  milk  drawn  at  different  milkings 
on  the  same  day.  The  fat  content  may  show  a  difference 
of  as  much  as  one  per  cent.  These  variations  are  attrib- 
uted to  change  in  the  character  of  the  feed,  or  in  the  time 
of  feeding  and  watering,  change  of  milkers,  the  weather, 
change  of  stable,  and  unusual  occurrences  (storms,  stran- 
gers, etc. ) .  The  quantity  of  milk  secreted  is  also  affected 
by  the  same  causes.  While  the  feed  has  no  pronounced 
permanent  effect  on  the  composition  of  the  milk,  a  change 
from  dry  to  green  feed  may  cause  a  temporary  increase 
in  the  fat  of  from  0.5  to  1  per  cent.,  while  distillery  slops 


22  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

or  other  very  watery  feed  may  cause  a  temporary  de- 
crease of  from  0.25  to  0.5  per  cent. 

The  time  of  milking  will  influence  the  composition  of 
milk.  When  the  intervals  between  the  milkings  are 
equal  and  the  feed,  amount  of  water,  etc.,  are  the  same, 
there  is  no  difference  between  the  composition  of  the 
morning  and  evening  milk;  but  in  practice  the  periods 
are  usually  unequal,  the  shorter  interval  preceding  the 
morning  milking  in  the  summer  and  the  evening  milking 
in  winter.  At  the  milking  following  the  shorter  interval 
the  quantity  of  milk  obtained  is  less  and  the  fat  per 
cent,  is  greater  than  at  the  other  milking.  Hence  it  fol- 
lows that  in  summer  the  morning's  milk  is  richer  in  fat 
but  of  lesser  quantity  than  the  evening's  milk,  while  in 
winter  the  reverse  is  true.  The  age  of  the  cow  has  no 
appreciable  effect  on  the  composition  of  milk.  Volun- 
tary exercise  in  the  open  air  increases  the  fat  per  cent, 
as  well  as  the  quantity  of  milk  yielded;  forced  exercise 
decreases  the  water  in  the  milk  and  consequently  de- 
creases the  volume  of  the  milk  flow,  but  the  per  cent,  of 
fat  is  increased,  while  violent  exercise  reduces  both  the 
volume  and  the  per  cent,  of  solids.  The  effects  of  cestrum 
are  not  uniform ;  the  fat  may  be  increased  or  decreased, 
the  albumin  may  be  increased  to  such  an  extent  that  the 
milk  will  curdle  when  boiled,  or  there  may  be  no  change 
in  the  composition.  In  one  test  of  milk  from  a  cow  with 
nympliomania  the  proteids  were  increased  to  5.72  per 
cent.  Weaning,  or  removing  the  calf,  when  it  causes  the 
cow  to  become  restless  and  fretful,  is  attended  with  a 
decrease  in  the  fat  per  cent.  The  variations  in  quantity 
and  composition  caused  by  disease  will  be  considered  in 
the  chapter  on  the  "  Influence  of  Disease  on  Milk." 

Market  Milk  varies  less  in  composition  than  indi- 


MILK  23 

vidual  milk,  because  the  different  variations  in  the  milk 
of  individual  cows  balance  one  another  more  or  less. 
Under  certain  conditions,  milk  from  different  herds,  i.e., 
herd  milk,,  may  show  a  greater  variation  in  composition 
than  the  mixed  milk  of  several  herds.  For  example,  milk 
from  a  Jersey  or  Guernsey  herd  will  usually  show  a 
higher  fat  content  than  milk  from  a  Holstein  or  Ayr- 
shire herd.  The  presence  of  a  large  proportion  of  "fresh" 
cows  in  a  herd  at  one  time  may  cause  the  mixed  milk 
of  the  herd  to  be  low  in  solids,  especially  fat,  while  a 
large  proportion  of  "strippers"  may  have  the  opposite 
effect.  The  per  cent,  of  fat  in  market  milk  may  range 
from  3  to  5  per  cent.,  and  the  per  cent,  of  solids  not 
fat  from  8.5  to  10.5  per  cent.  The  average  composition, 
as  reported  by  Flieschmann,  is :  fat,  3.4  per  cent. ;  lactose, 
4.6  per  cent.;  casein,  3  per  cent.;  albumin,  0.5  per  cent.; 
globulin,  a  trace;  salts,  0.75  per  cent.;  water,  87.75  per 
cent. 

Over  5000  samples  of  milk  examined  at  the  New 
York  State  Experiment  Station  at  Geneva,  N.  Y.,  were 
found  to  contain  an  average  of  3.9  per  cent,  of  fat, 
5.1  per  cent,  of  lactose,  2.5  per  cent,  of  casein,  0.7  per 
cent,  of  albumin,  0.7  per  cent,  of  salts,  and  87.1  per  cent, 
of  water. 

Although  it  is  unusual,  normal  market  milk  may  fall 
below  the  usual  limit  for  solids,  especially  fat,  particu- 
larly milk  from  a  single  herd,  under  some  of  the  condi- 
tions mentioned  above.  For  this  reason,  difficulty  has 
at  times  been  experienced  in  legally  proving  that  milk 
has  been  skimmed  or  diluted  with  skimmed  milk  or  water, 
and  this  has  led  to  the  adoption  of  legal  standards  for 
milk  and  other  dairy  products  by  different  states,  the 
United  States  government,  and  some  municipalities. 


24 


PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 


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25 


26  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

The  standard  of  the  United  States  Department  of 
Agriculture  calls  for  3.25  per  cent,  of  fat  and  8.5  per 
cent,  solids  not  fat  for  milk;  9.25  per  cent,  solids  for  skim 
milk,  and  18  per  cent,  fat  for  cream.  The  standards  for 
milk  and  other  dairy  products  adopted  by  the  various 
states  and  territories,  as  reported  by  the  United  States 
Bureau  of  Animal  Industry,  will  be  found  on  pages 
24  and  25. 

Reaction. — The  reaction  of  milk  is  amphoteric  to  lit- 
mus — i.e.,  it  turns  blue  litmus  red  (acid  monobasic  phos- 
phates) and  changes  red  litmus  to  blue  (alkaline  di- 
basic phosphates).  To  phenolphthalein  solution  it  is 
acid.  When  phenolphthalein  solution  is  added  to  milk, 
no  color  reaction  occurs,  because  the  color  of  phenol- 
phthalein solution  is  not  changed  by  acids.  But  if,  after 
the  addition  of  phenolphthalein  solution,  sodium  hydrox- 
ide solution  is  added  to  the  milk  in  excess  of  the  amount 
necessary  to  neutralize  the  acidity  the  fluid  assumes  a 
pink  color,  which  is  permanent.  This  reaction  is  made 
use  of  in  determining  the  degree  of  acidity  of  milk  and 
cream. 

To  neutralize  the  acidity  in  100  c.c.  of  normal,  fresh 
market  milk,  18  to  19  c.c.  of  a  one-tenth  normal  solution 
of  sodium  hydroxide  are  required.  This  represents  an 
acidity  of  0.16  to  0.17  per  cent.  The  acidity  of  milk 
when  it  is  drawn  from  the  udder  is  less  than  0.1  per  cent. 
This  original  or  native  acidity  is  due  to  the  casein  and 
acid  phosphates.  The  fermentation  of  the  milk  sugar 
by  bacteria  increases  the  acidity.  Lactic  or  other  acids 
formed  in  this  manner  are  present  whenever  the  acidity 
is  over  0.1  per  cent.  Market  milk  with  an  acidity  of  0.1 
to  0.2  per  cent,  is  considered  fresh  and  good.  In  some 


MILK  27 

cities  the  legal  limit  is  0.2  per  cent.    A  sour  taste  is  not 
present  until  the  acidity  exceeds  0.3  per  cent. 

The  acidity  of  colostrum  is  about  three  times  as  great 
as  that  of  milk.  As  the  colostrum  changes  to  milk,  the 
acidity  gradually  decreases  until  it  reaches  the  point 
normal  for  milk.  Toward  the  end  of  lactation  the  acidity 
is  further  decreased,  and  in  "strippers"  is  very  low,  or 
the  reaction  may  even  be  alkaline. 

The  reaction  of  the  milk  of  individual  cows  is  usually 
below  normal  in  acidity,  or  may  even  be  alkaline,  in  ordi- 
nary inflammations  of  the  udder,  tuberculosis  of  the 
udder,  and  probably  also  when  the  udder  is  eliminating 
abnormal  substances,  as  in  cowpox;  but  this  is  by  no 
means  always  the  case.  In  streptococcic  mastitis  the 
milk  may  be  more  acid  than  normal.  The  reaction  alone 
of  the  milk  of  individual  cows  cannot  therefore  be  relied 
upon  to  discover  diseased  conditions.  It  is  hardly  neces- 
sary to  mention  that  nothing  can  be  learned  on  this  point 
from  determining  the  reaction  of  market  milk. 

High  acidity  in  market  milk  is  usually  the  result  of 
excessive  fermentation  of  the  lactose,  and  is  an  indication 
that  the  milk  is  stale,  or  was  produced  under  unclean 
conditions,  or  was  not  properly  cooled  and  cared  for. 
The  addition  of  boric  acid  or  formaldehyde  also  increases 
the  acidity.  Salicylic  acid  has  less  effect  on  the  reac- 
tion because  it  is  usually  not  added  in  very  great  quan- 
tity. The  acidity  may  be  reduced  by  the  addition  of  alka- 
lies (bicarbonate  of  soda,  chalk,  potash) ,  but  the  addition 
of  these  substances  to  milk  is  illegal.  Addition  of  water 
and  heating  (loss  of  CO2)  also  reduce  the  acidity. 

(For  methods  of  determining  acidity,  see  pages  254 
to  257.) 


28          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 
PHYSICAL  PROPERTIES 

The  physical  properties  of  milk  which  are  of  great- 
est importance  in  milk  hygiene  are  the  color,  odor  and 
taste,  specific  gravity,  and  refraction.  Other  physical 
properties  which  have  been  extensively  studied  are  the 
viscosity,  surface  tension,  freezing  point,  and  electrical 
conductivity. 

Color. — Milk  is  a  white,  opaque  fluid,  sometimes  with 
a  yellowish  or  bluish  tinge.  The  white  color  is  due  to 
the  calcium  caseinate,  while  the  opacity  is  due  in  part  to 
the  same  substance  and  in  part  to  the  fat.  Not  only  the 
quantity  of  fat,  but  also  the  size  of  the  fat  globules, 
affects  the  opacity,  the  opacity  being  less  when  the  glo- 
bules are  large  than  when  they  are  small.  Since  opacity 
does  not  depend  entirely  on  the  quantity  of  fat,  tests  for 
fat  based  upon  transparency,  such  as  the  lactoscope  test 
(p.  239),  are  not  accurate.  The  yellowish  tinge  of  milk 
is  due  to  a  pigment  in  the  fat  (carotin) ;  it  is  more  pro- 
nounced in  milk  from  cows  of  certain  breeds,  as  the 
Guernseys.  A  bluish  tinge  indicates  that  the  milk  has 
a  low  fat  per  cent.,  and  is  sometimes  associated  with  skim- 
ming and  watering,  but  it  must  be  remembered  that  any 
milk  in  a  thin  layer  has  a  bluish  tinge. 

Odor  and  Taste. — Normal  milk  has  a  slight  odor, 
resembling  the  exhalations  from  the  cow's  skin,  and  a 
slightly  sweetish  taste.  During  the  colostral  period  and 
near  the  end  of  lactation,  individual  cow's  milk  may  have 
a  salty,  bitter.,  or  a  rancid,  animal-like  taste.  A  large 
proportion  of  "strippers"  in  a  herd  may  give  the  mixed 
milk  a  similar  taste.  The  milk  of  the  individual  cow  may 
also  be  salty  or  bitter  in  advanced  pregnancy,  after  abor- 
tion, in  mastitis,  and  when  digestion  is  disturbed.  Milk 
with  a  certain  degree  of  acidity  will  acquire  a  bitter, 


MILK  29 

astringent  taste  in  rusted  vessels  in  consequence  of  the 
formation  of  iron  lactate.  A  "fishy"  taste  may  also  be 
present  when  the  milk  vessels  are  rusty  or  when  they 
have  not  been  rinsed  free  of  soap  powder. 

Certain  aromatic  feeds  impart  a  characteristic  odor 
and  taste  to  the  milk.  Among  these  are  ensilage,  rape, 
cabbage,  and  beets,  turnips,  rutabagas,  carrots,  and  their 
tops.  This  is  not  ordinarily  due  to  the  ingestion  with  the 
feed  of  substances  responsible  for  the  taste  and  odor  and 
their  elimination  with  the  milk  through  the  udder,  but 
to  the  absorption  by  the  milk  of  the  odor  of  the  feed  from 
the  air  of  the  stable.  This  is  demonstrated  by  the  fact 
that  when  these  feeds  are  fed  in  ordinary  quantity  and 
after  milking,  and  not  immediately  before  or  during 
milking,  the  odor  and  taste  of  the  milk  are  not  affected. 
If  these  feeds  are  given  in  large  quantity,  it  is  probable 
that  some  of  the  aromatic  substances  may  be  excreted 
through  the  udder.  In  the  case  of  garlic,  however,  the 
volatile  oil  to  which  the  odor  of  that  substance  is  due  is 
eliminated  through  the  udder  in  the  milk.  Odors  are 
readily  absorbed  by  milk,  especially  when  it  is  warm. 
Milk  drawn  and  allowed  to  stand  in  an  unclean  or  poorly 
ventilated  stable  will  acquire  a  stable-like  odor  and  taste. 
It  has  been  demonstrated  experimentally  that  if  milk 
at  a  temperature  of  14  to  22°  C.  (57  to  72°  F.)  is  ex- 
posed to  the  odor  of  ensilage  or  horse  manure  for  a  half 
hour  to  an  hour  and  a  half  it  will  acquire  an  odor  and 
taste  resembling  these  substances  (Russell). 

Abnormal  odors  and  tastes  result  also  from  the 
growth  of  bacteria  in  milk.  The  activity  of  the  pepton- 
izing  bacteria  may  produce  first  a  bitter  taste,  due  to 
the  production  of  peptone,  and  later  a  foul  and  unpleas- 
ant odor  and  taste,  the  result  of  decomposition  processes. 


30          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Bacilli  of  the  coli-aerogenous  group  may  produce  an 
unclean,  even  nauseating,  taste  with  a  stable  or  manure- 
like  odor,  while  the  lactic  acid  bacteria  give  to  milk  a 
sour  odor  and  taste.  Specific  organisms  have  been  iden- 
tified which  produce  bitter,  soapy,  oily,  and  burnt  tastes 
and  a  stable-like  odor  and  taste.  Other  bacteria  produce 
a  rancid  odor  and  taste,  and  some  produce  an  unclean 
odor  and  taste.  While  some  of  the  peptonizing  bacteria 
(udder  cocci)  are  normal  inhabitants  of  the  udder,  the 
other  bacteria  usually  enter  the  milk  after  it  is  drawn 
from  the  cow.  Sometimes,  however,  bacteria  which  are 
the  cause  of  abnormal  odors  and  tastes  become  estab- 
lished in  the  udder.  Odors  and  tastes  of  bacterial  origin 
are  often  not  apparent  until  a  certain  period  after  the 
milk  has  been  taken  from  the  udder  and  usually  become 
more  pronounced  as  the  milk  increases  in  age.  Milk 
acquires  a  cooked  taste  when  heated  above  68  to  71°  C. 
(155  to  160°  F.)  Heating  in  open  vessels  has  a  more 
pronounced  effect  on  the  taste  than  heating  in  closed 
vessels  or  bottles. 

The  senses  of  smell  and  taste  tire  very  quickly  and 
cannot  be  depended  upon  to  judge  many  samples  of 
milk.  Odors  and  tastes  are  more  apparent  when  the 
milk  is  warm. 

Specific  Gravity. — As  would  naturally  be  expected 
from  the  statements  made  in  regard  to  the  variation  in 
the  composition  of  milk,  the  specific  gravity  or  density 
of  different  samples  of  milk  varies  considerable.  The 
range  of  variation  is  greater  for  individual  milk  than 
for  market  milk.  The  specific  gravity  of  the  milk  of 
individual  cows  will  range  from  1.027  to  1.040,  while 
that  of  market  milk  will  fluctuate  between  1.028  and 
1.034,  with  an  average  of  1.032,  at  the  standard  tempera- 


MILK  31 

ture  of  15°  C.  (60°  R).  At  higher  temperatures  the 
specific  gravity  or  density  is  decreased,  and  at  lower  tem- 
peratures it  is  increased. 

The  specific  gravity  depends  not  only  upon  the  total 
quantity  of  solids  contained  in  the  milk,  but  also  upon  the 
relative  proportion  in  which  the  individual  solids  are 
present,  because  the  individual  solids  are  of  different  spe- 
cific gravity.  Fat  shows  the  greatest  difference,  being 
much  lighter  than  the  other  solids ;  it  is  even  lighter  than 
water.  The  solids  not  fat  are  all  heavier  than  water, 
the  specific  gravity  of  the  salts  being  4.12,  lactose  1.666, 
and  proteids  1.346  (Richmond) .  Therefore  the  removal 
of  fat,  i.e.,  skimming,  increases  the  specific  gravity,  and 
the  addition  of  skim  milk  has  the  same  effect,  while  the 
addition  of  water  reduces  the  specific  gravity.  But  the 
specific  gravity  has  such  a  wide  normal  variation  that 
it  is  possible  to  remove  a  small  amount  of  fat  from  milk 
with  a  normally  low  specific  gravity  without  causing  the 
specific  gravity  to  rise  above  the  normal  range,  and, 
conversely,  a  certain  amount  of  water  may  be  added  to 
milk  with  a  normally  high  specific  gravity  without  lower- 
ing the  specific  gravity  below  the  normal  limit.  How- 
ever, in  the  first  case  the  per  cent,  of  fat  will  be  decreased, 
and  in  the  second  there  will  be  a  decrease  in  both  the  per 
cent,  of  fat  and  of  solids  not  fat.  When  the  specific 
gravity  of  milk  is  raised  above  the  normal  by  skimming 
it  may  be  brought  within  the  normal  range  by  the  addi- 
tion of  water,  but  the  per  cent,  of  fat  and  of  solids  not 
fat  will  be  decreased.  Therefore,  in  examining  market 
milk  to  detect  skimming  or  the  addition  of  skimmed 
milk  or  water,  the  per  cent,  of  fat  and  of  solids  not  fat 
must  always  be  considered  in  connection  with  the  spe- 
cific gravity.  (For  method  of  determining  the  specific 


32          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

gravity,  see  page  228.)  Determination  of  the  specific 
gravity  of  the  milk  solids  and  of  the  per  cent,  of  fat 
in  the  milk  solids  will  assist  in  detecting  milk  which  has 
been  skimmed  or  skimmed  and  watered.  ( See  page  246 
for  methods.)  The  milk  solids  of  normal  market  milk 
have  a  specific  gravity  of  1.31  to  1.36,  and  the  per  cent, 
of  fat  in  the  milk  solids  is  20  to  34.  When  milk  is 
skimmed  or  skimmed  and  watered,  the  specific  gravity 
of  the  milk  solids  is  increased,  while  the  per  cent,  of  fat  in 
the  solids  is  decreased. 

The  influence  of  disease  on  the  specific  gravity  of 
individual  milk  is  not  constant,  but  the  specific  gravity 
is  usually  lowered.  However,  the  specific  gravity  of 
individual  cow's  milk  cannot  be  made  use  of  to  discover 
diseased  conditions,  because  milk  from  different  cows 
shows  such  great  variations  under  normal  conditions. 
The  specific  gravity  of  milk  is  lower  when  it  is  drawn 
from  the  udder  than  it  is  several  hours  later. 

Refraction. — Rays  of  light  passing  through  one  me- 
dium into  another  of  different  optical  density,  as  through 
air  into  milk,  are  broken  or  refracted  at  the  point  of  con- 
tact of  the  two  media.  The  degree  of  refraction,  or  the 
refractive  power  compared  with  that  of  air,  is  called 
the  refractive  index.  Since  the  calcium  caseinate  and 
fat  contained  in  milk  prevent  the  light  rays  from  passing 
through  it,  these  substances  must  be  removed  before  the 
refractive  index  can  be  determined.  The  refractive  index 
of  milk,  so-called,  is  really  the  refractive  index  of  the 
milk  serum  or  whey,  i.e.,  the  milk  minus  the  calcium 
caseinate  and  fat. 

The  refractive  power  of  the  milk  serum  depends  upon 
the  quantity  of  lactose  or  of  lactose  and  salts  present. 
Adding  water  to  milk  reduces  the  proportion  of  these 


MILK  33 

substances,  and  therefore  reduces  the  refractive  index. 
Hence  the  refractive  index  may  be  used  to  detect  watered 
milk.  (See  method  on  page  249.)  The  refractive  index 
of  normal  market  milk  ranges  from  1.3429  to  1.3445. 
On  the  scale  of  the  Zeiss  dipping  refractometer,  the 
reading  for  normal  milk  ranges  from  37.3  to  41.5. 

Viscosity  is  manifested  by  the  adherence  of  milk  to 
the  sides  of  a  glass  vessel.  It  increases  as  the  tempera- 
ture of  the  milk  is  lowered,  and  vice  versa.  It  is  de- 
creased by  skimming  and  by  the  addition  of  water.  Dur- 
ing the  colostral  period  and  near  the  end  of  lactation  it 
is  greater  than  at  other  times  during  the  lactation  period; 
it  is  also  increased  in  disease  or  injuries  of  the  genital 
organs,  especially  the  udder. 

Boiling  momentarily,  or  heating  for  a  longer  time 
at  lower  temperatures,  decreases  the  viscosity  of  milk, 
causing  it  to  appear  thinner  than  normal  raw  milk. 
Cream  heated  at  60°  C.  (140°  F.)  for  twenty  minutes 
appears  thinner  and  less  viscous  than  raw  cream  with 
the  same  fat  per  cent,  and  will  not  "whip"  readily.  Vis- 
cogen,  a  mixture  of  cane  sugar  and  lime,  has  been  added 
to  heated  cream  to  overcome  this  change.  This  prepara- 
tion has  also  been  used  to  increase  the  viscosity  of  raw 
cream  of  low  fat  per  cent.,  and  also  to  increase  the  con- 
sistency of  skimmed  or  watered  milk.  The  addition  of 
viscogen  to  cream  or  milk  is  illegal  unless  the  product  is 
sold  as  visco-cream  or  visco-milk.  The  specific  gravity 
of  watered  or  skimmed  milk  is  increased  by  the  addition 
of  viscogen,  and  the  per  cent,  of  solids  not  fat,  especially 
the  salts,  is  also  increased.  The  acidity  is  reduced. 

Starch  is  also  added  to  cream  to  increase  the  body 
or  consistency. 

Freezing  Point. — The  freezing  point  of  milk  is 
3 


34          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

—0.54  to  —0.57°  C.  (31.02  to  30.9°  F.) .  It  varies  with 
the  amount  of  the  dissolved  substances  contained  in  the 
milk,  especially  the  salts.  When  water  is  added  to  milk 
the  freezing  point  rises,  while  in  disease  it  is  sometimes 
lowered  and  sometimes  raised.  The  determination  of 
the  freezing  point  has  as  yet  proven  of  no  practical  value 
in  routine  milk  examination.  Surface  tension  and  elec- 
trical conductivity  are  likewise  of  no  practical  impor- 
tance. 

MICROSCOPICAL  APPEARANCE  OF  MILK  AND  MILK  SEDIMENT 

When  examined  under  the  microscope,  milk  is  found 
to  contain  numerous  fat  globules  with  a  few  cells,  cell 
fragments,  and  free  nuclei  scattered  among  them.  If 
a  small  quantity  of  milk  is  placed  in  a  sediment  tube  and 
centrifugalized,  only  a  part  of  the  cells  and  cell  remnants 
are  thrown  down  to  the  bottom  of  the  tube  with  the 
heavier  constituents  of  the  milk;  many  adhere  to  the 
fat  globules  and  are  carried  to  the  top,  while  the  others 
remain  in  the  intermediate  fluid.  According  to  Prescott 
and  Breed,  only  about  one-fourth  is  contained  in  the 
sediment,  one-half  being  in  the  cream  and  the  remainder 
in  the  milk.  Heating  the  milk  to  60°  C.  (140°  F.)  or 
above  before  centrifugalizing  will  increase  the  cellular 
content  of  the  sediment.  If  some  of  the  sediment  is 
spread  out  in  a  thin  layer  on  a  glass  slide,  dried  in  the 
air,  fixed  by  heating,  and  stained,  the  cellular  bodies  can 
be  more  readily  studied. 

Cellular  Content. — It  will  then  be  observed  that  the 
cells  are  of  two  principal  kinds:  leucocytes  and  epithe- 
lial cells.  The  leucocytes  are  of  the  polymorphonuclear 
and  lymphocyte  varieties,  while  the  epithelial  cells  are 
of  the  pavement,  cuboidal  and  cylindrical  types.  Fre- 


MILK  35 

quently  the  epithelial  cells  are  folded  on  themselves,  when 
they  appear  as  rounded,  oval,  or  irregular  shapes,  and 
sometimes  they  are  arranged  in  groups  like  the  petals  of 
a  flower.  Degenerated  and  disintegrated  cells,  free  nu- 
clei, bacteria,  and  vegetable  cells  and  fibres  may  also 
be  present. 

Number  of  Cells. — The  number  of  cells  in  different 
samples  of  milk  will  vary  very  much.  Milk  from  indi- 
vidual cows  in  normal  condition  may  contain  from  50,000 
to  1,000,000  and  over  per  c.c.  (Savage).  Milk  from 
the  same  cow  may  show  considerable  differences  when 
examined  at  intervals  of  a  week  or  a  month,  and  varia- 
tions may  also  be  found  in  the  milk  from  different  quar- 
ters of  the  udder  of  the  same  cow.  The  number  of  cells 
may  differ  at  different  stages  of  the  same  milking,  being 
much  greater  in  the  end  milk  than  in  the  first  milk. 

The  cellular  content  is  very  high  for  a  few  days  after 
calving.  Near  the  end  of  lactation  the  cells  again  in- 
crease in  number,  and  they  are  also  present  in  excess 
after  incomplete  or  delayed  milking.  In  mastitis  there 
is  usually  a  pronounced  increase  in  the  number  of  cells, 
particularly  the  leucocytes.  In  some  cases  the  number 
is  as  high  as  200,000,000  to  300,000,000  per  c.c.  (Sav- 
age), but  in  others  it  is  as  low  as  500,000  per  c.c.  The 
cell  content  of  milk  from  an  udder  affected  with  mastitis 
exhibits  two  other  features  which  are  important,  viz: 
the  cells  are  clumped  or  grouped  together,  and  75  to  80 
per  cent,  are  polymorphonuclear  leucocytes.  Red-blood 
cells  may  also  be  present  in  the  milk  when  the  udder  is 
very  much  congested,  as  may  occur  at  the  beginning  of 
lactation  and  in  acute  inflammation,  and  also  following 
traumatic  injuries. 

The  differences  in  the  cell  content  of  the  individual 


36  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

milk  of  normal  cows  are  likely  to  balance  one  another 
when  the  milk  of  several  cows  is  mixed  together;  con- 
sequently different  samples  of  market  milk  show  less 
variation  in  the  number  of  leucocytes  than  individual 
milk.  On  the  other  hand,  when  the  milk  from  one  cow 
affected  with  mastitis  is  mixed  with  the  milk  of  other 
cows  in  the  herd  which  are  in  normal  condition,  the  cell 
content  of  the  mixed  milk  is  not  likely  to  be  very  much 
increased  unless  the  herd  is  a  very  small  one  or  the  milk 
from  the  diseased  cow  contains  an  enormous  number  of 
cells. 

Several  methods  have  been  devised  for  detecting  an 
excessive  number  of  cells  in  milk  (see  pages  281  to  284) . 
When  used  to  examine  the  milk  of  individual  cows, 
these  methods  are  of  great  assistance  in  discovering  cases 
of  mastitis  before  clinical  symptoms  or  visible  milk 
changes  appear,  but  when  applied  to  samples  of  mixed 
market  milk  they  cannot  be  depended  upon  entirely  for 
the  purpose  of  detecting  mastitis  in  the  herds  supplying 
the  milk. 

BIOLOGICAL  PROPERTIES  OF  MILK 

Ferments  or  Enzymes. — Milk  contains  a  number  of 
ferments  or  enzymes.  Some  of  them  resemble  the  di- 
gestive ferments  in  their  action.  This  class  includes  a 
proteolytic  ferment  called  galactase,  and  diastase,  an 
amylolytic  ferment.  These  ferments  are  believed  to 
assist  in  the  digestion  of  milk.  A  tripsin-like  ferment 
and  fat-splitting  ferments  or  lipases  have  been  reported, 
but  their  existence  is  questioned.  There  are  also  oxidiz- 
ing ferments :  the  oxydases  and  peroxydase,  and  reduc- 
ing ferments:  catalase  and  reductase.  The  diastase, 


MILK  37 

peroxydase,  catalase,  and  reductase  reactions  have  been 
made  use  of  in  milk  control  work. 

Original  and  Bacterial  Ferments. — In  milk  hygiene 
it  is  important  to  distinguish  between  original  and  bac- 
terial ferments.  An  original  ferment  is  one  which  is 
secreted  by  the  cells  of  the  udder,  or  which  is  contained 
in  cells  like  the  leucocytes  and  becomes  free  in  the  milk 
when  these  cells  disintegrate.  A  bacterial  ferment  is 
secreted  by  the  bacteria  which  gain  access  to  milk  after 
it  is  formed  in  the  udder.  A  bacterial  ferment  increases 
in  quantity  after  milk  is  drawn  from  the  udder  as  a  result 
of  the  growth  of  bacteria,  and  if  it  is  destroyed  by  heat 
it  will  again  appear  unless  the  bacteria  are  all  killed  and 
the  milk  is  not  reinf  ected.  On  the  other  hand,  an  original 
ferment  cannot  increase  in  quantity  after  the  milk  leaves 
the  udder,  and  if  it  is  destroyed  by  heat  it  does  not  reap- 
pear in  the  milk.  Diastase  and  peroxydase  are  original 
ferments,  catalase  is  both  an  original  and  a  bacterial 
ferment,  and  reductase  is  a  bacterial  ferment. 

Diastase. — One  hundred  c.c.  of  normal  milk  will  di- 
gest 0.015  to  0.02  gramme  of  starch  in  thirty  minutes. 
This  action  is  due  to  an  amylolytic  ferment  contained  in 
the  milk,  which  has  been  called  diastase.  This  ferment 
operates  best  at  a  temperature  of  45°  C.  (113°  F.)  and 
is  destroyed  by  a  temperature  of  65  to  68°  C.  (149  to 
154°  F.)  for  thirty  minutes.  It  is  present  in  the  milk 
when  it  is  formed  in  the  udder,  and  is  therefore  an  orig- 
inal ferment.  It  is  not  produced  by  bacteria.  Colostrum 
is  richer  in  diastase  than  ordinary  milk,  and  the  ferment 
is  also  present  in  greater  quantity  near  the  end  of  lac- 
tation. The  end  milk  contains  more  diastase  than  the 
first  milk  drawn  from  the  udder.  (See  diastase  test  on 
page  297.) 


38  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Peroxydase. — If  paraphenyldiamin  or  tincture  of 
guaiac  is  added  to  milk  with  a  little  hydrogen  peroxide, 
the  milk  at  once  assumes  a  blue  color.  This  change 
occurs  because  the  ferment  contained  in  the  milk  called 
"  peroxydase "  splits  off  oxygen  from  the  hydrogen 
peroxide  and  this  free  oxygen  oxidizes  the  paraphenyl- 
diamin or  the  guaiac  to  a  colored  compound.  If  the  milk 
is  heated  to  80°  C.  (176°  F) ,  the  reaction  does  not  occur 
because  the  ferment  is  destroyed.  The  reaction  occurs 
best  at  40  to  50°  C.  (104  to  122°  F.).  Peroxydase  is 
present  in  milk  when  it  is  formed  in  the  udder  and  it  is 
not  secreted  by  bacteria.  It  is  therefore  an  original 
ferment.  (See  tests  for  heated  milk  on  page  298.) 

Catalase. — This  ferment,  which  is  also  known  as 
superoxidase,  possesses  the  specific  property  of  splitting 
up  hydrogen  peroxide  into  water  and  oxygen.  The  re- 
action which  occurs  is  as  follows :  2H2O2  =*  2H2O  +  O2. 
Catalase  is  both  an  original  and  a  bacterial  ferment.  It 
is  secreted  with  the  milk  and  is  contained  in  leucocytes 
and  in  blood.  It  is  also  secreted  by  many  of  the  bacteria 
found  in  milk,  but  the  various  species  differ  in  their 
capacity  to  produce  the  ferment.  The  putrefactive  or- 
ganisms appear  to  produce  it  in  the  greatest  quantity. 
The  ability  of  the  lactic  acid  bacteria  to  produce  catalase 
is  in  dispute. 

The  amount  of  catalase  in  milk  as  it  comes  from  the 
udder  varies  at  different  stages  of  lactation.  The  cata- 
lase content  is  high  during  the  colostral  period  and  this 
condition  usually  continues  for  three  weeks,  although  in 
exceptional  cases  it  falls  to  the  amount  normal  for  milk 
by  the  fourth  or  fifth  day  after  parturition.  Near  the 
end  of  lactation,  when  the  milk  has  fallen  to  about  a 
quart  per  day  or  less,  the  catalase  again  increases.  Some 


MILK  39 

observers  report  that  no  increase  occurs  duing  oestum, 
but  others  state  that  when  the  cow  is  nervous  and  excitable 
the  catalase  is  sometimes  increased.  Pronounced  changes 
in  the  feed  may  affect  the  quantity  of  catalase.  The 
first  milk  drawn  at  a  milking  contains  less  catalase  than 
the  end  milk. 

When  milk  is  separated,  the  greater  portion  of  the 
catalase  passes  over  into  the  cream.  Skim  milk,  there- 
fore, has  a  very  low  catalase  content.  After  milk  has 
reached  a  certain  degree  of  acidity  (about  0.36  per  cent.) , 
the  acid  begins  to  exert  an  inhibitory  influence  on  the 
activity  of  the  catalase.  Up  to  this  point  the  catalytic 
activity  is  increased  because  the  amount  of  catalase  is 
increased  by  bacterial  growth.  In  milk  which  has  under- 
gone "  sour  curdling,"  the  catalase  is  paralyzed  by  the 
acid  and  is  inactive.  The  catalytic  activity  may  be  re- 
stored to  such  milk  by  neutralizing  it  with  lime  water. 

When  milk  is  exposed  to  a  low  temperature  in  winter 
or  to  prolonged  refrigeration,  the  catalase  is  partially  or 
completely  destroyed.  Catalase  operates  best  at  a  tem- 
perature of  37°  C.  (98.6°  F.) .  The  lethal  temperature  is 
around  68°  C.  (154°  F.),  but  varies  within  wide  limits 
according  to  the  source  of  the  catalase.  Heated  milk 
may  be  reactivated,  since  catalase  is  a  bacterial  as  well 
as  an  original  ferment.  ( See  catalase  test  on  pages  287 
to  294.) 

Reductase. — If  a  small  quantity  of  methylene  blue 
solution  is  added  to  milk,  the  mixture  will  be  colored 
blue,  but  the  blue  color  will  disappear  after  a  time  because 
the  methylene  blue  is  reduced  and  converted  into  its 
leuco-base.  This  change  is  brought  about  by  a  ferment 
in  the  milk  called  reductase.  If  formalin  is  added  to  the 
methylene  blue  solution,  forming  what  is  known  as  Schar- 


40          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

dinger's  reagent,  and  a  little  of  this  solution  is  added  to 
milk,  the  mixture  will  also  be  colored  blue,  but  the  color 
will  disappear  more  rapidly.  At  first  the  difference  in 
the  time  of  reduction  was  attributed  to  the  difference  in 
the  composition  of  the  solution,  but  further  research 
demonstrated  the  presence  in  milk  of  two  different  re- 
ducing agents.  The  ferment  which  reduces  themethylene 
blue  solution  is  called  "  M-reduetase,"  while  the  one 
which  reduces  the  formalin-methylene  blue  solution  has 
been  named  "  FM-reductase." 

M-Reductase. — This  ferment  is  not  secreted  in  the 
udder  with  the  milk.  It  is  generally  regarded  as  of 
bacterial  origin,  although  the  opinion  has  been  expressed 
(Burri  and  Kursteiner)  that  the  cellular  elements  of 
milk,  like  all  living  protoplasm,  have  a  reduction  power 
and  that  the  high  reduction  power  of  colostrum  during 
the  first  day  after  parturition  and  of  mastitis  milk  is  due 
to  the  rich  cellular  content  of  these  secretions.  It  has 
been  well  established,  however,  that  the  capacity  of  milk 
to  reduce  methylene  blue  increases  with  the  number  of 
bacteria. 

The  different  species  of  bacteria  vary  in  their  reduc- 
tion power.  Reduction  power  appears  to  depend  first 
upon  the  species,  then  upon  the  number  of  bacteria,  and, 
finally,  upon  the  media  in  which  the  organisms  are  grow- 
ing. The  anaerobic  organisms  usually  have  a  greater 
reduction  power  than  the  aerobes,  while  the  facultative 
anaerobes  act  more  powerfully  in  the  absence  of  oxygen 
than  when  it  is  present.  The  colon  bacilli  belong  to  the 
facultative  anaerobes  of  high  reduction  power.  On  the 
other  hand,  the  reduction  power  of  the  lactic  acid  bacteria 
is  weak.  Different  samples  of  fresh  milk  containing 
about  the  same  number  of  bacteria  may  differ  greatly  in 


MILK  41 

reduction  power  because  of  the  difference  in  the  species 
of  bacteria  present.  But,  according  to  B'arthel  and  O. 
Jensen,  when  milk  is  stored  under  suitable  conditions, 
the  relative  proportion  of  the  different  species  of  bac- 
teria present  is  almost  always  changed  in  favor  of  the 
lactic  acid  organisms,  so  that  in  the  case  of  market  milk 
there  is  usually  correspondence  between  the  reduction 
time  and  the  number  of  bacteria. 

The  reduction  power  of  a  microorganism  is  not  con- 
stant, but  depends  upon  the  vitality  of  the  organism;  it 
will  therefore  decrease  with  the  age  of  the  organism  and 
also  when  nutritive  conditions  are  unfavorable.  Hence, 
the  reduction  activity  of  milk  rich  in  bacteria  is  relatively 
less  than  milk  containing  fewer  bacteria.  These  factors 
render  the  reductase  test  less  exact  than  the  plate  method 
for  estimating  the  number  of  bacteria  in  market  milk, 
but  not  for  judging  the  "  keeping  qualities  "  of  the 
milk,  since  the  more  vitally  active  the  contained  bacteria 
the  more  rapidly  will  the  milk  undergo  bacterial  decom- 
position. 

The  reduction  power  of  cream  is  greater  than  that 
of  skim  milk.  The  reduction  power  is  greatest  just  be- 
fore curdling.  In  curdling,  the  ferment  is  precipitated 
with  the  curd.  The  ferment  operates  best  at  a  tem- 
perature of  40  to  55°  C.  (104  to  131°  F.)  and  is 
destroyed  by  a  temperature  of  70  to  80°  C.  (158  to 
176°  F.). 

FM-Reductase. — The  knowledge  concerning  this 
ferment  is  not  sufficiently  definite  at  this  time  to  be  of  any 
value  in  the  practice  of  milk  hygiene.  FM-reductase 
is  present  in  colostrum  on  the  first  day  after  parturition 
and  is  then  absent  from  the  udder  secretion  for  two  to 
three  weeks,  when  it  again  appears  in  the  milk.  Schern 


42  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

therefore  proposed  the  FM-reductase  test  as  a  means  of 
determining  whether  or  not  a  cow  is  "  fresh."  FM- 
reductase  is  absent,  or  present  only  in  very  small  quan- 
tity, in  the  first  milk  drawn  at  a  milking,  but  it  is  always 
present  in  the  end  milk.  After  stasis  of  milk,  it  is  absent. 
The  reaction  cannot  be  used  for  the  detection  of  mastitis, 
because  while  reduction  occurs  rapidly  in  some  cases,  in 
others  it  occurs  more  slowly  than  in  normal  milk  or  may 
not  occur  at  all. 

Antibodies  or  Immune  Bodies. — Antibodies  are  sub- 
stances which  are  produced  in  the  animal  body  to  pro- 
tect it  from  the  action  of  bacteria  or  their  toxins.  The 
term  includes  antitoxins,  agglutinins,  precipitins,  op- 
sonins,  lysins  (amboceptors) ,  complement,  etc.  Comple- 
ment is  always  present  in  the  blood  and  the  other  kinds 
of  antibodies  are  also  contained  in  the  normal  serum  in 
a  non-specific  form,  but  these  antibodies  do  not  appear  in 
the  blood  in  a  specific  form  until  after  the  body  is  invaded 
by  pathogenic  organisms  or  their  toxins. 

It  has  been  demonstrated  that  antitoxins,  agglutinins, 
and  opsonins  pass  over  from  the  blood  into  the  milk  when 
the  udder  is  in  a  normal  condition.  B  act erio-ly sins  are 
eliminated  in  the  milk  when  the  udder  is  aif  ected  with 
mastitis  and  during  the  colostral  stage,  but  it  is  doubtful 
if  they  pass  over  from  the  blood  into  the  milk  under  nor- 
mal conditions  at  other  times.  Complement  is  present 
in  colostrum  and  also  in  milk  when  the  udder  is  affected 
with  mastitis.  It  may  be  present  in  normal  milk  for  as 
long  as  twenty-six  days  after  parturition,  but  after  that 
time  it  is  absent,  according  to  some  observers.  The  com- 
plement demonstration  test  has  not  come  into  general 
use  for  the  detection  of  mastitis  principally  because  cer- 


MILK  43 

tain  investigators  have  reported  that  complement  is 
always  present  in  milk  from  apparently  normal  cows. 

The  quantity  of  antibodies  in  the  milk  compared  with 
the  quantity  circulating  in  the  blood  is  not  definitely 
known.  The  question  has  been  more  extensively  studied 
in  connection  with  antitoxins  than  with  the  other  anti- 
bodies, and  it  was  found  that  the  milk  contains  only  one- 
thirtieth  to  one-fifteenth  of  the  quantity  of  antitoxin 
circulating  in  the  blood.  Agglutinins  may  be  present 
in  the  milk  in  the  same  quantity  as  in  the  blood,  or  in 
greater  or  less  amount.  The  immunizing  value  of  the 
milk  has  not  been  completely  determined.  It  has  been 
demonstrated  that  antibodies  in  milk  ingested  by  suck- 
lings are  absorbed  through  the  intestines  into  the  blood 
when  the  suckling  and  the  animal  from  which  the  milk 
is  obtained  are  of  the  same  species.  There  is  no  direct 
evidence,  however,  that  the  antibodies  are  absorbed  into 
the  blood  of  the  young  animal  when  the  milk  is  from  a 
different  species,  as  when  a  child  ingests  cow's  milk,  al- 
though many  observations  have  been  made  which  indicate 
that  antibodies  are  absorbed  under  such  circumstances, 
if  only  to  a  limited  extent.  It  would  therefore  appear 
that  antibodies  in  cow's  milk  are  of  more  value  to  the 
calf  than  to  a  child  ingesting  such  milk.  The  absorption 
of  antibodies  from  the  intestines  is  greatest  during  the 
first  few  days  after  birth  and  decreases  with  age.  In 
older  animals,  the  antibodies  are  split  up  by  digestion 
like  other  proteids. 

Germicidal  Action  of  Milk. — Milk  from  cows  in  normal 
condition  always  contains  antibodies  which  destroy  many 
of  the  bacteria  commonly  present  in  milk.  The  intensity 
and  duration  of  this  germicidal  action  varies  with  the 
temperature.  If  the  milk  is  kept  at  37°  C.  (98.6°  F.), 


44          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

there  will  be  a  decided  decrease  in  the  number  of  bacteria 
for  the  first  six  hours  after  the  milk  is  drawn  from  the 
cow;  at  26  to  29°  C.  (79  to  84°  F.)  the  decrease  is  less 
rapid,  but  continues  for  eight  to  ten  hours,  and  at  15°  C. 
( 60  °  F. )  it  is  still  further  reduced  in  rate  but  continues  for 
about  twenty- four  hours  (Rosenau  and  McCoy).  The 
effect  of  the  same  milk  on -different  species  of  bacteria  is 
different,  and  the  effect  of  different  milks  on  the  same 
species  of  bacteria  also  varies,  showing  that  the  antibodies 
are  specific  for  certain  species  of  bacteria.  The  germie- 
idal  power  of  milk  is  not  capable  of  destroying  all  bac- 
teria which  may  gain  access  to  milk  during  milking  and 
the  subsequent  handling;  hence  precautions  against  bac- 
terial contamination  together  with  proper  cooling  are 
none  the  less  necessary.  It  is  also  incapable  of  always 
preventing  the  development  of  pathogenic  bacteria. 
These  organisms  may  enter  the  teat  canal  and  milk  cistern 
and  even  invade  the  gland  alveoli.  Heating  milk  for 
thirty  minutes  to  56°  C.  (133°F.)  considerably  weakens 
the  germicidal  property,  and  it  is  entirely  destroyed  by  a 
temperature  of  70°  C.  (158°  F.),  or  above,  for  thirty 
minutes.  Bacteria,  therefore,  grow  more  rapidly  in 
heated  milk  than  in  fresh  raw  milk.  The  germicidal 
power  of  colostrum  and  of  milk  from  cows  affected  with 
mastitis  is  greater  than  that  of  normal  milk. 

Toxins. — It  has  been  demonstrated  that  tetanus  toxin 
may  be  eliminated  in  the  milk  of  a  cow  affected  with 
tetanus,  and  in  sufficient  quantity  to  kill  mice  fed  with 
the  milk  (Miessner).  There  is,  therefore,  reason  to  be- 
lieve that  other  bacterial  toxins  are  also  eliminated  in 
the  milk,  although  there  is  no  direct  proof.  However, 
the  quantity  of  toxin  circulating  in  the  blood  is  very 
small,  even  in  severely  infected  animals,  and  only  a 


MILK  45 

minute  quantity  could  be  eliminated  in  the  milk.  When 
it  is  considered  in  addition  that  the  milk  secretion  ceases 
in  severely  affected  animals,  the  danger  from  toxins 
eliminated  in  the  milk  is  very  slight.  Toxins  may  be 
produced  by  bacteria  growing  in  milk  after  it  is  drawn 
from  the  udder.  There  is  evidence  to  show  that  toxins 
are  very  readily  absorbed  through  the  gastro-intestinal 
mucous  membrane  of  young  animals.  Toxins  in  milk 
from  a  different  species  are  absorbed  with  much  less 
facility  than  when  the  milk  is  from  the  same  species. 
Diphtheria  and  tetanus  toxins  have  been  given  to  adult 
animals  by  the  mouth  in  large  quantities  without  any 
harmful  effect,  the  toxins  apparently  being  split  up  in 
the  process  of  digestion  like  other  proteids.  These,  how- 
ever, are  soluble  toxins  (exogenous)  which  are  more 
susceptible  to  chemicals  and  ferments  than  endotoxins. 
What  may  happen  when  the  digestive  processes  are  de- 
ranged, or  when  wounds  are  present  in  the  mucous  mem- 
brane, is  not  known.  Milk  from  animals  affected  with 
rabies  contains  the  virus  of  the  disease,  but  such  milk  does 
not  produce  rabies  when  ingested  if  the  mucous  mem- 
brane of  the  digestive  tract  is  intact  and  the  gastric  secre- 
tion is  normal. 

Aggressins  and  other  substances  which  inhibit  the 
protective  reaction  of  the  body  against  the  action  of  bac- 
teria and  their  toxins  have  also  been  demonstrated  in 
milk. 

CLASSES  OR  GRADES  OF  MARKET  MILK 

Until  quite  recently  no  effort  was  made  to  establish 
uniform  grades  or  classes  of  milk.  In  some  instances, 
the  terms  sanitary  milk,  hygienic  milk*  aerated  milk, 
baby's  milk,  nursery  milk,  etc.,  have  been  applied  by  dis- 
tributers to  some  of  the  milk  sold  by  them,  but  these 


46  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

terms  are  very  indefinite  and  have  been  frequently  used 
indiscriminately.  Since  1893,  milk  produced  under  the 
supervision  of  a  medical  milk  commission  has  been  sold 
under  the  name  of  certified  milk,  but  the  term  has  also 
been  applied  to  milk  which  was  not  produced  under  these 
conditions.  The  desirability  of  defining  the  special 
names  used  for  milk,  and  the  advantage  to  both  the  pro- 
ducer and  consumer  of  grading  or  classifying  market 
milk  according  to  its  hygienic  quality,  has  long  been 
recognized,  but  no  definite  steps  were  taken  in  the  matter 
until  1907  when  Melvin1  proposed  that  market  milk 
be  graded  in  three  classes,  as  follows : 

Class  1.  Certified  Milk. — This  may  be  briefly  defined  as  milk 
produced  in  accordance  with  the  requirements  of  the  American 
Association  of  Medical  Milk  Commissions  (see  Appendix). 

Class  2.  Inspected  Milk. — This  term  should  be  limited  to 
clean  raw  milk  from  healthy  cows,  as  determined  by  the  tuber- 
culin test  and  physical  examination  by  a  qualified  veterinarian. 
The  cows  are  to  be  fed,  watered,  housed,  and  milked  under  good 
conditions,  but  not  necessarily  equal  to  the  conditions  provided 
for  Class  1.  All  persons  who  come  in  contact  with  the  milk 
must  exercise  scrupulous  cleanliness,  and  must  not  harbor  the 
germs  of  typhoid  fever,  tuberculosis,  diphtheria,  and  other  in- 
fections liable  to  be  conveyed  by  the  milk.  This  milk  is  to  be 
delivered  in  sterilized  containers,  and  is  to  be  kept  at  a  tempera- 
ture not  exceeding  50°  F.  until  it  reaches  the  consumer.  It  shall 
contain  not  more  than  100,000  bacteria  per  cubic  centimetre. 

Class  3.  Pasteurized  Milk. — Milk  from  the  dairies  not  able 
to  comply  with  the  requirements  specified  for  Classes  1  and  2 
is  to  be  pasteurized  before  being  sold,  and  must  be  sold  under 
the  designation  "  pasteurized  milk."  Milk  for  pasteurization 
shall  be  kept  at  all  times  at  a  temperature  not  exceeding  60°  F. 
while  in  transit  from  the  dairy  farm  to  the  pasteurization  plant, 

1  24th  Annual  Report,  U.  S.  Bureau  of  Animal  Industry, 
pp.  179  to  182. 


MILK  47 

and  milk  after  pasteurization  should  be  placed  in  sterilized  con- 
tainers and  delivered  to  the  consumer  at  a  temperature  not 
exceeding  50°  F.  All  milk  of  an  unknown  origin  should  be 
placed  in  Class  3  and  subjected  to  clarification  and  pasteuriza- 
tion. No  cow  in  any  way  unfit  for  the  production  of  milk  for 
use  by  man,  as  determined  upon  physical  examination  by  an 
authorized  veterinarian,  and  no  cow  suffering  from  a  com- 
municable disease  should  be  permitted  to  remain  on  any  dairy 
farm  on  which  milk  of  Class  3  is  produced,  except  that  cows 
which  upon  physical  examination  do  not  show  physical  signs  of 
tuberculosis  may  be  included  in  dairy  herds  supplying  milk  of 
this  class.  This  milk  is  to  be  clarified  and  pasteurized  at  cen- 
tral pasteurization  plants,  which  shall  be  under  the  personal 
supervision  of  an  officer  or  officers  of  the  health  department. 
These  pasteurizing  plants  may  be  provided  either  by  private 
enterprise  or  by  the  municipality,  and  should  be  located  within 
the  city. 

A  further  attempt  at  classification  was  made  in  1911 
by  a  commission  on  milk  standards  appointed  by  the  New 
York  Milk  Committee.  This  commission  recommended 
that  milk  be  graded  in  four  classes,  viz. :  Class  A,  certi- 
fied milk  or  its  equivalent;  Class  B,  inspected  milk;  Class 
C,  pasteurized  milk,  and  Class  D,  milk  not  suitable  for 
drinking  purposes.  A  year  later,  however,  the  commis- 
sion presented  a  second  report 1  in  which  the  following 
classification  was  recommended: 

GRADE  A 

Raw  MUk. — Milk  of  this  class  shall  come  from  cows  free 
from  disease  as  determined  by  tuberculin  tests  and  physical 
examinations  by  a  qualified  veterinarian,  and  shall  be  produced 
and  handled  by  employees  free  from  disease  as  determined  by 

1  Reprint  No.  141  from  the  Public  Health  Reports,  Aug.  22, 
1913. 


48          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

medical  inspection  of  a  qualified  physician,  under  sanitary  con- 
ditions such  that  the  bacterial  count  shall  not  exceed  100,000 
per  cubic  centimetre  at  the  time  of  delivery  to  the  consumer.  It 
is  recommended  that  dairies  from  which  this  supply  is  obtained 
shall  score  at  least  80  on  the  United  States  Bureau  of  Animal 
Industry  score  card. 

Pasteurized  Milk. — Milk  of  this  class  shall  come  from  cows 
free  from  disease  as  determined  by  physical  examinations  by  a 
qualified  veterinarian  and  shall  be  produced  and  handled  under 
sanitary  conditions  such  that  the  bacterial  count  at  no  time  ex- 
ceeds 200,000  per  cubic  centimetre.  All  milk  of  this  class  shall 
be  pasteurized  under  official  supervision,  and  the  bacterial  count 
shall  not  exceed  10,000  per  cubic  centimetre  at  the  time  of 
delivery  to  the  consumer.  It  is  recommended  that  dairies  from 
which  this  supply  is  obtained  shall  score  at  least  65  on  the 
United  States  Bureau  of  Animal  Industry  score  card. 

The  above  represents  only  the  minimum  standards  under 
which  milk  may  be  classified  in  Grade  A.  The  commission  recog- 
nizes, however,  that  there  are  grades  of  milk  which  are  produced 
under  unusually  good  conditions,  in  especially  sanitary  dairies, 
many  of  which  are  operated  under  the  supervision  of  medical 
associations.  Such  milks  clearly  stand  at  the  head  of  this  grade. 

GRADE   B 

Milk  of  this  class  shall  come  from  cows  free  from  disease 
as  determined  by  physical  examinations,  of  which  one  each  year 
shall  be  by  a  qualified  veterinarian,  and  shall  be  produced  and 
handled  under  sanitary  conditions  such  that  the  bacterial  count 
at  no  time  exceeds  1,000,000  per  cubic  centimetre.  All  milk  of 
this  class  shall  be  pasteurized  under  official  supervision,  and  the 
bacterial  count  shall  not  exceed  50,000  per  cubic  centimetre 
when  delivered  to  the  consumer. 

It  is  recommended  that  dairies  producing  Grade  B  milk 
should  be  scored  and  that  the  health  departments  or  the  con- 
trolling departments,  whatever  they  may  be,  strive  to  bring 
these  scores  up  as  rapidly  as  possible. 


MILK  49 

GRADE    C 

Milk  of  this  class  shall  come  from  cows  free  from  disease 
as  determined  by  physical  examinations  and  shall  include  all 
milk  that  is  produced  under  conditions  such  that  the  bacterial 
count  is  in  excess  of  1,000,000  per  cubic  centimetre. 

All  milk  of  this  class  shall  be  pasteurized,  or  heated  to  a 
higher  temperature,  and  shall  contain  less  than  50,000  bacteria 
per  cubic  centimetre  when  delivered  to  the  consumer. 

Whenever  any  large  city  or  community  finds  it  necessary, 
on  account  of  the  length  of  haul  or  other  peculiar  conditions, 
to  allow  the  sale  of  Grade  C  milk,  its  sale  shall  be  surrounded 
by  safeguards  such  as  to  insure  the  restriction  of  its  use  to 
cooking  and  manufacturing  purposes. 

In  1917  the  commission  published  a  third  report r  in 
which  the  above-mentioned  grades  were  again  recom- 
mended with  the  same  specifications  for  each  grade  ex- 
cept that  the  bacterial  limit  for  Grade  A,  raw  milk,  was 
reduced  from  100,000  to  10,000  bacteria  per  c.c.  This 
is  an  extremely  low  bacterial  limit  for  market  milk  to 
be  used  for  general  purposes  and  it  is  very  doubtful  if 
it  can  be  adopted  by  any  community  without  consider- 
ably reducing  the  supply  of  raw  milk  and  increasing  its 
cost  to  the  consumer.  Certified  milk  meets  the  demand 
for  a  milk  of  low  bacterial  content  for  special  purposes, 
such  as  infant  feeding,  etc. 

1  Public  Health  Reports,  Vol.  32,  No.  7,  Feb.  16, 1917. 


CHAPTER  IV 

BACTERIA  OF  MILK 

UNLESS  drawn  under  special  conditions,  which  are 
not  obtainable  in  dairy  practice,  milk  always  contains 
bacteria.  Some  of  them  come  from  the  udder ;  others  are 
derived  from  the  cow's  skin,  the  dust  of  the  fodder  and 
litter,  the  milk  vessels  and  utensils,  the  person  and  cloth- 
ing of  the  milker,  etc.,  and  enter  the  milk  during  the 
process  of  milking  and  in  the  subsequent  handling  of 
the  milk.  They  are,  under  normal  conditions,  non-patho- 
genic organisms,  and,  since  they  are  always  present  in 
milk,  are  called  the  common  milk  bacteria.  Under  cer- 
tain conditions,  which  are  discussed  in  another  chapter, 
milk  contains  also  pathogenic  bacteria. 

COMMON  MILK  BACTERIA 

Some  of  the  non-pathogenic  bacteria  do  not  bring 
about  any  perceptible  change  in  milk.  Many  of  them, 
however,  produce  marked  alterations,  and  it  is  because 
of  their  presence  that  milk  is  so  extremely  perishable  or 
unstable.  In  growing  in  milk,  these  organisms  split  up 
certain  constituents,  notably  the  lactose  and  casein,  into 
various  products,  some  of  which  are  capable  of  exerting 
an  injurious  effect  upon  persons  drinking  the  milk,  par- 
ticularly children  and  invalid  adults.  Certain  of  these 
changes,  including  the  more  harmful  kinds,  may  be  con- 
siderably advanced  before  they  are  indicated  by  any  alter- 
ation in  the  appearance,  odor,  or  taste  of  the  milk.  There- 
fore, while  the  common  milk  bacteria  are  in  themselves 
harmless,  and  while  their  growth  in  milk  to  a  limited 

50 


BACTERIA  OF  MILK  51 

extent  is  not  attended  with  any  appreciable  injurious 
effects,  their  presence  in  large  numbers  is  not  desirable 
because  it  may  be  accompanied  by  harmful  results. 

There  are  numerous  species  of  these  organisms.  For 
facility  of  study  as  well  as  for  practical  purposes,  it  is 
convenient  to  group  them  according  to  the  changes  which 
they  bring  about  in  milk.  Although  some  of  the  species 
which  ferment  lactose  produce  both  acids  and  gases,  and 
although  a  part  of  those  which  act  principally  upon  the 
lactose  also  operate  upon  the  casein  in  a  lesser  degree 
and  vice  versa,  nevertheless  by  grouping  the  different 
species  according  to  their  dominant  effect  a  very  clear 
conception  is  obtained  of  the  important  changes  produced 
in  milk  by  the  organisms  of  each  group.  Following  this 
plan,  the  numerous  species  of  common  milk  bacteria  may 
be  classified  in  the  following  groups: 

1.  Acid-forming  Bacteria. — These  organisms  split 
up  the  lactose  in  milk  and  form  acids.  The  milk  first 
acquires  a  sour  odor  and  taste  and  later  curdles.  This 
is  the  most  quickly  apparent  change  which  occurs  in 
milk.  The  acids  combine  with  the  calcium  of  the  calcium 
caseinate,  and  the  casein,  being  thus  set  free,  is  precipi- 
tated in  the  form  of  a  smooth,  white  jelly-like  curd,  which 
may  contain  a  few  gas  bubbles  or  furrows  made  by 
ascending  bubbles.  In  the  beginning,  the  curd  is  dry  and 
is  equal  in  size  to  the  original  volume  of  the  milk,  but 
later  on  it  contracts  and  expresses  a  fluid  or  serum  which 
holds  in  solution  certain  of  the  milk  constituents. 

The  time  required  for  milk  to  sour  and  curdle  depends 
upon  the  number  and  kind  of  acid-forming  bacteria  it 
contains  and  the  temperature  at  which  it  is  kept.  On 
the  average,  about  0.45  per  cent,  acidity  is  necessary  to 
bring  about  curdling.  The  acid-forming  bacteria  con- 


52  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

tinue  to  grow  and  to  ferment  lactose  until  the  acidity 
reaches  0.8  per  cent.,  but  the  growth  of  other  bacteria 
stops  when  the  acidity  exceeds  0.2  per  cent.  The  acid- 
forming  bacteria,  therefore,  perform  the  very  important 
service  of  inhibiting  the  growth  of  the  more  harmful 
bacteria.  If  their  development  is  interfered  with,  the 
milk  will  undergo  putrefaction  instead  of  souring. 

Sour  milk  is  not  harmful  to  healthy  adults;  on  the 
contrary,  in  certain  forms  (curds  and  whey,  buttermilk, 
kefir,  etc.)  it  is  a  regular  article  of  diet,  and  milk  contain- 
ing certain  acid-forming  bacteria  is  beneficial  in  some 
diseased  conditions.  But,  nevertheless,  milk  in  which  the 
fermentation  is  not  sufficiently  advanced  to  cause  coagu- 
lation or  even  to  produce  an  appreciable  sour  taste  may 
cause  vomiting  and  indigestion  in  small  children  and  in 
persons  affected  with  catarrh  of  the  stomach. 

The  usual  cause  of  the  spontaneous  curdling  of  milk 
is  the  Bacterium  lactis  acidi  (Fig.  5) ,  also  called  Strepto- 
coccus lacticus,  which  occurs  as  a  coccus  or  as  a  short  oval 
or  pointed  bacterium,  arranged  in  pairs,  frequently  in 
short  and  sometimes  in  long  chains,  and  forms  on  solid 
media  very  small,  white,  circular  or  lenticular  colonies, 
many  of  them  being  situated  below  the  surface.  In  addi- 
tion to  the  difference  in  form,  variations  occur  in  the 
ability  to  ferment  lactose  and  in  other  biological  char- 
acters. These  are  regarded  by  some  bacteriologists  as 
changes  due  to  environment,  while  others  consider  them 
a  sufficient  basis  for  recognizing  the  existence  of  different 
varieties  or  species.  In  general,  however,  organisms  of 
the  Streptococcus  lacticus  type  ferment  lactose  more 
rapidly  than  the  other  species  of  acid-forming  bacteria, 
forming  principally  lactic  acid,  with  little  or  no  gas.  The 
milk  has  a  clean,  sour  taste,  while  the  fluid  expressed  from 


BACTERIA  OF  MILK 


531 


the  curd  is  clear.  Being  commonly  concerned  in  the 
souring  of  milk  and  producing  principally  lactic  acid, 
the  organisms  of  this  type  are  known  as  the  true  lactic 
acid  bacteria.  The  Streptococcus  lacticus  must  not  be 
confused  with  the  mastitis  streptococci  (Fig.  6),  which 
also  ferment  lactose  and  have  other  corresponding  char- 
acteristics. The  latter  organisms  grow  in  long,  inter- 
twined chains,  the  individual  members  of  which  are  rec- 
tangular or  oval  in  form,  with  the  long  axis  at  right 


FIG.  5.  —  Preparation  showing  Streptococ- 
ens  lacticus  or  Bacterium  lactis  acidi. 


Fia.  6.  —  Preparation  from  sediment 
obtained  by  centrif  ugalizing  milk  from  a 
cow  a  fleeted  with  catarrhal  mastitis,  show- 
ing streptococci  and  leucocytes. 


angles  to  the  length  of  the  chain.    On  agar,  they  form 
extremely  minute,  punctiform,  brownish  colonies. 

The  Bacterium  acidi  lactici  (  Hueppe)  ,  also  called  the 
Bacillus  lactis  aerogenesf  is  frequently  concerned  in  the 
spontaneous  souring  of  milk,  usually  in  association  with 
the  Streptococcus  lacticus.  This  is  a  short,  plump,  non- 
motile  bacterium  which  is  closely  related  to  the  coli-aero- 
genes  group  of  bacteria  and  may  be  regarded  as  the  most 
active  acid-forming  member  of  that  group.  It  grows 
upon  the  surface  of  solid  media,  forming  thin,  partially 
translucent,  leaf-shaped  colonies,  or  round  semi-globular 


54  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

colonies.  It  ferments  lactose  more  slowly  and  requires 
a  higher  temperature  than  the  Streptococcus  lacticus. 
Acetic  acid  is  the  principal  product  of  the  lactose  fermen- 
tation, although  lactic  and  succinic  acids  and  gas  are 
also  formed.  Gas  bubbles  are  rather  numerous  in  the 
curd  and  the  fluid  expressed  from  the  latter  is  not  always 
clear.  The  sour  taste  of  the  milk  is  frequently  un- 
pleasant. The  Bacterium  acidi  lactici  is  regarded  by  some 
bacteriologists  as  a  distinct  species  with  strains  showing 
differences  resulting  from  environment  and  by  others 
as  the  type  of  a  number  of  species  or  varieties.  The 
mastitis  organisms,  Bacillus  Guillebeau  (a  and  b)9  and 
some  of  the  bacteria  which  produce  slimy  or  viscid  milk 
are  closely  related  forms. 

Several  varieties  of  long,  thin,  rod-shaped  organisms, 
of  which  the  Bacterium  bulgaricus  is  a  type,  also  form 
acid  from  lactose,  but  they  operate  so  slowly  at  the  usual 
temperatures  that  they  are  not  a  factor  in  the  ordinary 
souring  of  milk.  They  are  chiefly  of  interest  because  of 
their  use  in  the  preparation  of  the  oriental  milks  (mazun, 
kefir,  yoghurt) .  The  organisms  of  the  Bacterium  bul- 
garicus group  are  usually  present  in  ensilage  and  those 
found  in  milk  are  no  doubt  derived  directly  or  indirectly 
from  this  source. 

The  temperature  at  which  the  milk  is  kept  has  an 
important  influence  upon  the  character  of  the  lactose 
fermentation.  In  milk  kept  at  15  to  20°  C.  (59  to  68° 
F. ) ,  the  organisms  of  the  Streptococcus  lacticus  type  will 
grow  much  more  rapidly  than  those  of  the  Bacterium 
acidi  lactici  type.  The  Streptococcus  lacticus  grows  quite 
well  at  15°  C.  (59°  F.)  and  continues  to  grow  at  10° 
C.  (50°  F.) ,  while  the  Bacterium  acidi  lactici  grows  bet- 
ter at  higher  temperatures  and  practically  stops  grow- 


FIG.  7. — Colonies  of  coli  aerogenes  bacteria  (Weigmann). 


FlG.  8. — Colonies  of  Proteus  vulgaris,  natural  size  (Weigmann). 


BACTERIA  OF  MILK  55 

ing  at  15°  C.  (59°  F.).  Keeping  milk  at  a  tempera- 
ture of  15°  C.  (59°  F.)  or  below,  therefore,  inhibits  the 
least  desirable  type  of  lactose  fermentation.  The  Bacil- 
lus bulgaricus  requires  a  temperature  of  at  least  25°  C. 
(77°  F.). 

The  acid-forming  bacteria  are  widely  distributed,  but 
according  to  Esten  1  the  chief  primary  source  of  those  of 
the  Streptococcus  lacticus  type  found  in  milk  is  the  cow's 
mouth.  The  organisms  are  present  in  the  manger  and  on 
everything  within  reach  of  the  cow's  mouth,  also  in  the 
fasces.  The  acid-formers  of  the  Bacterium  acidi  lactici 
type  are  derived  from  sugar-containing  grain  and  roots 
like  corn,  beets,  and  carrots,  especially  when  they  are  cut 
into  small  pieces,  packed  and  fermented  (ensilage) ;  they 
are  also  contained  in  the  fasces  of  cows  (Weigmann). 
Milk  vessels  and  utensils,  and  other  things  and  places 
with  which  milk  comes  in  contact  become  seeded  with 
acid-forming  bacteria  when  not  properly  cleaned  and 
sterilized,  and  are  usually  the  principal  sources  of  con- 
tamination when  these  organisms  are  present  in  milk  in 
excessive  numbers. 

2.  Gas-forming  Bacteria. — Included  in  this  group  are 
the  bacteria  which  ferment  the  lactose  in  milk  and  form 
gases  in  addition  to  acids.  They  also  decompose  the 
proteids  to  some  extent,  especially  the  casein  (Fig.  7). 
Most  of  them  belong  to  the  large  coli-aerogenes  group 
of  organisms.  The  milk  is  curdled  in  the  form  of  a 
smooth,  white,  jelly-like  curd,  which  is  more  or  less  per- 
meated with  gas  bubbles  and  is  associated  with  some 
fluid.  The  aerogenes  organisms  form  a  greater  quantity 
of  acids  and  gases  than  the  coli  and  they  also  form  more 

1  "  Bacterium  Acidi  Lactici  and  Its  Sources,"  Storr's  Agr. 
Expt.  Sta.  Bull.  No.  59. 


56  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

lactic  acid  than  the  coli,  but  the  latter  are  more  active  in 
proteid  decomposition.  Carbon  dioxide,  hydrogen,  car- 
buretted  hydrogen,  and  nitrogen  are  the  gases  produced, 
while  the  acids  formed  are  lactic,  acetic,  and  succinic.  In 
the  early  stages  of  this  change,  the  milk  has  a  sweetish- 
sour  refreshing  taste  and  an  odor  that  is  not  unpleasant, 
especially  when  the  aerogenes  bacteria  are  operating,  but 
later  the  taste  is  unclean,  while  the  odor  is  stable-like,  and 
finally  the  taste  becomes  nauseating  and  salty  and  the 
odor  is  like  that  of  decomposing  manure  and  urine.  Milk 
undergoing  this  form  of  fermentation  and  decomposition 
may  prove  harmful  to  persons  drinking  it,  especially  in- 
fants and  adults  with  weak  digestion. 

The  principal  representatives  of  this  group  of  bac- 
teria are  the  Bacillus  coli  and  the  Bacillus  aerogenes^  also 
called  Bacillus  lactis  aerogenes  and  Bacterium  acidi  lac- 
tici  (Hueppe).  The  Bacillus  coli  is  a  short,  thick,  oval 
organism,  which  is  motile,  and  which  forms  on  solid  media 
colonies  which  are  usually  flat,  leaf-shaped  and  partially 
translucent,  sometimes  moist  and  globular.  Some  vari- 
eties render  the  milk  alkaline  and  do  not  curdle  it  nor 
produce  any  other  visible  change;  others  peptonize  the 
casein.  Several  varieties  of  coli  are  pathogenic,  e.g.,  the 
bacilli  of  calf  cholera,  the  Bacillus  enteritidis  (Gartner) 
and  the  Bacillus  phlegmasia  uberis,  which  is  one  of  the 
causes  of  parenchymatous  mastitis  according  to  Kitt. 
The  Bacillus  lactis  aerogenes  or  Bacterium  acidi  lactici 
(Hueppe),  described  previously  in  connection  with  the 
acid-forming  bacteria,  may  be  regarded  as  a  type  of  the 
aerogenes  bacteria,  of  which  there  are  a  number  of 
varieties. 

The  optimum  temperature  of  the  coli-aerogenes  bac- 
teria is  37°  C.  (98.6°  F.),  but  they  grow  quite  well  at 


BACTERIA  OF  MILK  57 

lower  temperatures  down  to  20°  C.  (68°  F.).  They  do 
not  grow  as  well  as  the  Streptococcus  lacticus  between 
15  and  20°  C.  (59  and  68°  F.),  and  at  lower  tempera- 
tures the  difference  is  still  greater. 

These  organisms  are  normal  inhabitants  of  the  in- 
testines of  the  cow  and  consequently  are  hardly  ever  en- 
tirely absent  from  milk.  They  are  present  in  water  pol- 
luted by  drainage  from  barnyards,  manure  heaps  and 
cesspools,  and  also  on  field  crops,  especially  roots  grown 
on  manured  ground.  Their  presence  in  milk  in  any 
considerable  number  indicates  that  it  has  been  contami- 
nated with  manure  or  with  polluted  water. 

Milk  also  contains  anaerobic  bacteria  which  ferment 
lactose  and  its  salts,  forming  gas  in  large  quantity  and 
producing  strong-smelling  acids  like  butyric,  valerianic 
and  propionic.  These  organisms  are  present  ordinarily 
in  small  number  and  their  development  is  usually  pre- 
vented by  the  acid-forming  bacteria.  When  they  grow 
in  milk  in  large  numbers,  a  curd  containing  many  gas 
bubbles  is  formed.  The  milk  has  the  odor  of  the  acid 
produced  and  frequently  an  odor  of  putrefaction  also. 
Because  of  the  latter  condition,  these  organisms  are  re- 
garded as  putrefactive  bacteria.  The  best  known  are 
those  which  produce  butyric  acid  and  are  consequently 
called  butyric  acid  bacteria.  They  are  very  large  spore- 
forming  bacilli  which  live  in  cultivated  soil  in  symbiosis 
with  the  peptonizing  bacteria.  They  are  usually  present 
in  the  spore-forming  stage  on  the  products  of  the  field. 
Morphologically,  they  are  distinguished  from  the  other 
spore-forming  milk  bacteria  by  a  change  in  form  during 
spore  formation,  becoming  shuttle-shape,  drum-stick- 
shape,  etc. 

Ayers  and  Johnson  found  gas-forming  bacteria  in 


58  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

milk  which  were  not  members  of  the  coli-aerogenes  group 
but  which  were  apparently  spore-formers,  having  sur- 
vived a  temperature  of  93.3°  C.  (200°  F.)  for  thirty 
minutes.1 

3.  Peptonizing  or  Casease  Bacteria. — The  bacteria 
of  this  group  are  also  known  as  liquefiers  and  are  the  cause 
of  decay  and  putrefaction  in  general.  They  secrete 
two  enzymes  or  ferments  which  attack  the  proteids  of 
milk,  especially  the  casein.  One  is  a  rennet-like  ferment 
which  acts  upon  the  calcium  casemate  in  the  same  manner 
as  rennet,  splitting  it  up  into  calcium  paracaseinate  and 
a  substance  called  whey-proteid.  The  calcium  para- 
caseinate being  insoluble,  it  is  precipitated  and  forms  a 
curd.  The  whey-proteid  remains  in  solution  in  the  whey, 
hence  the  name.  The  other  enzyme  is  casease,  a  proteo- 
lytic  ferment  resembling  trypsin,  which  digests  the  pro- 
teids in  the  curd  and  whey,  splitting  them  up  into  soluble 
compounds  like  albumoses  and  peptones  (peptonization) 
and  then  again  into  simpler  compounds  like  amino-acids 
and  ammonium  bases  (decomposition).  The  two  fer- 
ments are  produced  in  varying  proportions  by  different 
species  of  bacteria.  When  the  rennet-like  ferment  pre- 
dominates a  firm  white  curd  is  formed  and  is  slowly 
digested.  There  is  more  or  less  fluid  (whey)  present. 
As  digestion  proceeds,  the  curd  gradually  disappears  and 
is  replaced  by  a  turbid  fluid.  The  surface  of  the  curd  in 
contact  with  the  fluid  has  a  rough  or  fuzzy  appearance. 
When  the  proteolytic  ferment  (casease)  is  present  in 
greatest  quantity,  the  curd  is  soft,  flocculent  and 
"  mushy,"  or  coagulation  does  not  occur  at  all,  while 
peptonization  takes  place  rapidly.  In  the  earlier  stages 

1  B.  A.  I.  Bulletin  No.  161,  pp.  47  and  48. 


BACTERIA  OF  MILK  59 

of  this  type  of  decomposition,  the  milk  acquires  a  bitter 
taste  (peptones)  and  later  the  taste  and  odor  are  foul 
and  unpleasant.  Some  of  the  decomposition  products 
are  capable  of  exerting  an  injurious  effect  upon  persons 
drinking  the  milk.  Nausea  and  vomiting  may  occur, 
even  in  adults,  when  the  taste  is  only  bitter  and  before  it 
has  become  decidedly  foul.  The  reaction  of  the  milk  is 
usually  alkaline,  but  some  of  the  peptonizers  are  acid- 
formers  and  curdle  milk  by  souring  it. 

Included  in  this  group  are  certain  of  the  cocci  which 
appear  to  be  constantly  present  in  the  lower  parts  of  the 
cow's  udder  and  are  consequently  called  udder  cocci. 
These  organisms  are  to  be  found  regularly  in  milk  when 
it  comes  from  the  udder,  especially  in  the  fore  milk. 
They  are  present  in  greater  proportion  in  milk  produced 
under  good  conditions  than  in  ordinary  milk.  There  are 
many  varieties  or  species  of  these  organisms  which  differ 
principally  in  their  fermentative  properties  and  in  the  color 
of  their  colonies.  In  milk  hygiene,  it  is  desirable  to 
divide  them  into  peptonizers  and  non-pep tonizers.  Part 
of  the  peptonizers  first  curdle  milk  and  then  digest  the 
curd ;  others  bring  about  digestion  without  previous  cur- 
dling. Some  of  the  organisms  which  curdle  the  milk  do 
so  by  means  of  a  rennet-like  ferment ;  the  others  by  means 
of  acid  resulting  from  fermentation  of  the  lactose  (acid 
peptonizers) .  The  non-pep  tonizers  are  practically  inert, 
producing  no  apparent  change  in  milk.  On  agar  plates, 
the  udder  cocci  form  small,  irregularly  round  colonies 
which  are  usually  white.  The  colonies  of  Staphylococcus 
pyogenes  albus  vary  from  white  to  cream  color,  while 
those  of  Staphylococcus  pyogenes  aureus  are  orange- 
yellow.  The  latter  two  organisms  are  peptonizers  and 
also  form  lactic  acid.  The  ordinary  udder  cocci  and 


60  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Staphylococcus  pyogenes  albus  and  aureus  are  similar  in 
so  many  respects  that  all  are  regarded  by  some  bac- 
teriologists as  different  varieties  of  the  same  species. 
The  optimum  temperature  for  the  udder  cocci  is  35  to 
37°  C.  (95  to  98.6°  R),  but  they  grow  well  at  much 
lower  temperatures,  development  continuing  down  to 
freezing.  The  peptonizing  action  is  exerted  at  these 
low  temperatures. 

Many  of  the  peptonizers  are  spore-forming  bacteria. 
The  most  common  representatives  of  this  division  are 
the  hay  bacillus  (Bacillus  subtilis)  and  the  potato  bacillus 
(Bacillus  mesentericus  vulgatus).  They  belong  to  a 
large  group  of  organisms  which  are  very  numerous  in 
cultivated  soil  and  are  consequently  found  on  all  products 
of  the  soil,  especially  hay,  straw,  roots,  etc.  They  are 
large  rod-shaped  bacteria  with  rounded  ends.  The  spores 
form  in  the  middle  or  end  of  the  organism  without  chang- 
ing its  shape.  On  agar  plates  these  bacteria  form  dry, 
thin,  superficial  skin-like  colonies,  with  irregular  borders. 
The  colonies  have  a  tendency  to  extend  over  the  surface 
of  the  media  and  are  consequently  called  "  spreaders." 
These  organisms  are  very  numerous  in  the  dust  of  hay 
and  other  dry  fodder,  also  in  straw,  and  they  may  get 
into  the  milk  in  large  numbers  if  the  fodder  or  litter  is 
brought  into  the  stable  and  distributed  a  short  time  before 
milking,  or  if  dust  from  hay  or  other  dry  fodder  is  per- 
mitted to  sift  down  into  the  stable  through  cracks  in  the 
ceiling.  When  a  cow  lies  upon  bedding  or  upon  loose 
soil,  these  bacteria  enter  the  folds  and  creases  of  the 
skin  and  become  attached  to  the  hair,  and  when  the  cow 
is  milked  those  upon  the  udder,  flanks  and  surrounding 
parts  are  dislodged  and  may  fall  into  the  milk  pail. 
These  organisms  are  especially  numerous  on  the  hair 


BACTERIA  OF  MILK  61 

and  skin  of  cows  at  pasture.  The  manure  does  not  con- 
tain very  many  and  few  are  carried  into  milk  on  this 
substance  (Weigmann).  The  hay  and  potato  bacilli 
grow  best  at  23  to  37°  C.  (73  to  99.6°  R),  but  will  de- 
velop at  any  temperature  between  10  and  45°  C.  (50  to 
113°  F.) .  The  spores  are  very  resistant  to  heat  and  will 
survive  several  hours  boiling. 

Other  peptonizers  include  the  bacteria  of  the  proteus 
group  of  putrefactive  organisms,  which  are  often  present 
in  milk,  although  more  frequently  found  in  water  (Fig. 
8).  They  are  long,  thin  bacilli  which  grow  in  colonies 
of  various  forms.  The  most  common  representative  of 
these  organisms  is  the  Bacillus  pfoteus  vulgaris,  which 
grows  in  colonies  with  branches  or  ray-like  projections. 
They  get  into  the  milk  principally  through  the  water  used 
to  wash  the  milk  vessels  and  utensils.  The  Bacillus 
proteus  vulgaris  grows  best  at  about  25°  C.  (77°  F.) 

4.  Alkali-forming  Bacteria. — Some  of  the  bacteria 
commonly  found  in  milk  render  the  milk  alkaline  without 
producing  any  change  for  a  time  in  its  appearance,  taste, 
or  odor.     When  the  alkalinity  has  attained  a  certain 
degree,  the  fat  is  saponified  and  the  neutral  calcium 
caseinate  compound  becomes  basic,  in  consequence  of 
which  the  milk  is  changed  to  a  yellow,  translucent,  whey- 
like  fluid  (Jensen).    Within  the  ordinary  life  of  milk, 
however,  the  bacteria  of  this  group  are  practically  without 
effect.    Usually  they  get  into  the  milk  in  the  same  man- 
ner as  hay  bacilli  (page  60) ,  their  source  being  the  soil, 
but    occasionally    they    are    derived    from    the    faeces 
(Rogers). 

5.  Inert  Bacteria. — A  large  number  of  the  common 
milk  bacteria  produce  no  change  in  the  appearance,  odor, 
taste,  or  reaction  of  milk  and  are  consequently  said  to 


62  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

be  inert.  Many  bacteria  belong  to  this  group,  which  in- 
cludes some  of  the  udder  cocci.  Many  of  the  most  im- 
portant pathogenic  organisms  are  also  inert  in  so  far  as 
their  effect  on  milk  is  concerned,  notably  the  tubercle 
bacillus,  the  bacillus  of  typhoid  fever,  paracoli  or  para- 
typhus  bacilli,  and  the  diphtheria  bacillus.  The  presence 
of  these  harmful  organisms  is  not  indicated  by  any  ap- 
parent change  in  the  milk. 

VARIATIONS  IN  NUMBER  AND  KIND  OF  BACTERIA 

Different  samples  of  market  milk  may  show  the 
greatest  differences  in  the  number  and  kind  of  bacteria 
present.  One  sample  may  contain  much  fewer  than  1000 
bacteria  per  c.c.  and  another  may  contain  four  or  five 
million  and  even  more.  In  one  sample,  the  bacteria  may 
be  largely  of  the  inert  forms  and  in  another  the  bacteria 
of  the  gas-forming  group  may  predominate.  Market 
milk  containing  not  more  than  100,000  bacteria  per  c.c. 
is  considered  of  good  quality.  The  limit  for  certified 
milk  is  10,000  bacteria  per  c.c. 

The  kind  or  species  of  the  bacteria  must  be  considered 
as  well  as  the  number.  Generally,  the  smaller  the  num- 
ber of  bacteria  present  the  better  the  milk,  but  there  are 
exceptions  to  this  rule.  A  few  pathogenic  organisms 
would  be  more  harmful  than  a  much  larger  number  of 
the  common  milk  bacteria.  Between  the  different  groups 
of  the  latter  there  are  also  important  differences.  Milk 
containing  a  rather  large  number  of  bacteria  the  greater 
proportion  of  which  belong  to  the  inert  or  lactic  acid 
groups  is  less  objectionable  than  milk  containing  a 
smaller  number  of  bacteria  with  the  greater  proportion 
belonging  to  the  gas-f  orming  or  peptonizing  groups.  On 
the  other  hand,  while  milk  containing  a  large  percentage 


BACTERIA  OF  MILK  63 

of  peptonizing  bacteria  is  not  objectionable  when  the 
total  number  of  bacteria  is  small,  it  is  always  objection- 
able when  the  bacterial  count  is  high. 

The  number  of  bacteria  present  in  market  milk  de- 
pends upon  (1)  the  original  contamination,  (2)  the 
temperature  at  which  the  milk  has  been  kept,  and  (3) 
the  age  of  the  milk,  i.e.,  the  time  which  has  elapsed  since 
the  milk  was  drawn  from  the  cow. 

1.  By  original  contamination  is  meant  the  bacteria 
which  get  into  the  milk  during  milking  and  the  subse- 
quent handling  of  the  milk.    The  extent  of  this  depends 
upon  the  cleanliness  and  health  of  the  cows,  stable  prac- 
tices, method  of  milking,  cleanliness  of  the  milk  vessels 
and  utensils,  etc. 

2.  The  temperature  at  which  milk  is  kept  affects  not 
only  the  total  number  of  bacteria  but  also  influences  the 
relative  rate  of  increase  of  the  different  kinds  or  species. 
As  a  rule,  the  higher  the  temperature  the  more  rapidly 
the  bacteria  multiply.    For  example,  Conn  found  that 
when    fresh   milk    contained    6525    bacteria    per    c.c., 
after  25  hours  at  10°  C.  (50°  F.)  it  contained  6425  bac- 
teria per  c.c.,  while  after  25  hours  at  21°  C.  (70°  F.)  it 
contained  6,275,000  bacteria  per  c.c. 

When  milk  is  promptly  cooled  to  10°  C.  (50°  F.) 
and  held  at  that  temperature,  little  or  no  increase  of 
bacteria  will  occur  for  twenty-four  to  thirty-six  hours, 
and  even  at  15°  C.  (59°  F.)  the  increase  will  not  be 
very  great.  At  temperatures  above  20°  C.  (68°  F.), 
however,  the  bacteria  increase  very  rapidly. 

As  stated  above,  the  temperature  affects  not  only  the 
number  of  bacteria  but  also  the  relative  development  of 
the  different  species.  In  other  words,  it  determines  the 
type  of  fermentation  or  decomposition  which  the  milk 


64  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

will  undergo  with  age.  Most  species  of  bacteria  thrive 
best  at  about  body  temperature  (37  to  38°  C.,  98.6  to 
100.4°  F.),  but  at  lower  temperatures  some  multiply 
more  rapidly  than  others.  At  temperatures  below  15°  C. 
(59°  F.),  and  especially  below  10°  C.  (50°  F.),  the  or- 
ganisms of  the  peptonizing  group  develop  more  rapidly 
than  any  of  the  other  common  milk  bacteria.  At  15  to 
20°  C.  (59  to  68°  F.),  the  true  lactic  acid  bacteria  in- 
crease faster  than  any  of  the  others.  At  temperatures 
above  20°  C.  (68°  F.),  the  acid-forming  bacteria  may 
continue  to  multiply  more  rapidly  than  the  others,  but 
the  gas-formers  are  more  likely  to  increase  most  rapidly. 
The  higher  temperatures  are  also  favorable  to  the  de- 
velopment of  pathogenic  organisms. 

3.  The  age  of  milk  has  considerable  influence  on  the 
number  of  bacteria.  The  longer  the  period  which  has 
elapsed  since  the  milk  was  drawn  from  the  cow  the  more 
time  afforded  for  the  multiplication  of  the  bacteria  in- 
cluded in  the  original  contamination. 

(The  method  of  determining  the  number  of  bacteria 
is  described  on  pages  260  to  272.) 

Proportion  of  Different  Groups  of  Bacteria. — The 
kind  or  species  of  bacteria  included  in  the  original  con- 
tamination, and  the  relative  proportion  in  which  the 
different  groups  are  represented,  will  vary  with  the  con- 
ditions under  which  the  milk  is  produced.  In  milk  pro- 
duced under  good  conditions  and  examined  shortly  after 
it  was  drawn  from  the  cows,  Conn  found  that  the  greater 
portion  of  the  bacteria  are  udder  cocci,  including  both 
peptonizers  and  the  inert  variety.  Usually  1  or  2  per 
cent.,  sometimes  more,  are  lactic  acid  bacteria.  A  few 
gas-producing  bacteria  and  hay  and  potato  bacilli  are 
likely  to  be  present,  but  they  should  never  be  numerous. 


BACTERIA  OF  MILK  65 

The  kind  of  bacteria  which  will  predominate  in  milk  of 
this  kind  when  it  reaches  the  consumer  will  depend  upon 
the  temperature  at  which  it  is  kept  (see  above).  The 
fermentation  test  offers  a  rapid  and  convenient  method 
of  determining  the  kind  of  bacteria  which  predominates 
in  a  sample  of  milk  (see  page  278) . 

A  large  percentage  of  the  bacteria  present  in  market 
milk  belongs  to  the  inert  group.  This  is  shown  by  the 
following  table  compiled  from  examinations  reported  by 
Ayers  and  Johnson  * : 


No.  samples           Average             Percent, 
examined.         number  bac-      peptonizing, 
teria  per  c.  c. 

Percent. 
.    Alkali- 
forming. 

Percent, 
inert. 

Percent. 
Acid,  coag- 
ulating. 

Percent. 
Acid,  non- 
coagulating. 

12 

32,950,000 

17.31 

6.47 

29.31 

36.17 

10.71 

17 

3,451,000 

14.10 

19.66 

43.51 

12.98 

9.74 

24,700 

12.81 

3.33 

43.13 

33.85 

6.85 

1  B.  A.  I.  Bull.  161,  pp.20-27. 


CHAPTER  V 

MILK  DEFECTS 

IN  addition  to  the  changes  in  milk  caused  by  the 
common  milk  bacteria  and  those  occurring  in  the  course 
of  diseases  of  the  cow,  there  are  certain  alterations  in 
consistency,  odor,  taste,  and  color  which  are  known  as 
milk  defects.  Some  of  these  defects  make  the  milk  re- 
volting, even  nauseating,  while  a  few  render  it  harmful. 
They  may  be  divided  into  two  groups  (a)  those  which 
are  present  when  the  milk  is  drawn  from  the  udder  and 
(b)  those  which  appear  shortly  afterward. 

(a)  Milk  Defects  which  are  Present  in  Milk  when  it 
Comes  from  the  Udder. — The  most  important  of  these 
are  named  below,  together  with  the  causes,  the  latter 
being  given  because  they  indicate  the  measures  to  be  taken 
for  the  correction  or  removal  of  the  defects. 

1.  Cow-like  or  Salty,  Cow-like  Taste. — The  milk  has 
a  strong  cow-like  taste  or  a  salty,  cow-like  taste,  is  of  a 
gray  color  and  may  have  the  appearance  of  soapy  water. 
This  may  be  due  to  several  causes.  Milk  from  cows  in 
the  last  stages  of  lactation  has  a  mild,  cow-like  taste  which 
is  attributed  to  the  relaxation  of  the  gland  tissue  and  fil- 
tration of  blood  serum  between  the  epithelial  cells  of  the 
alveoli.  The  cow-like  taste  also  occurs  when  the  cow 
has  been  incompletely  milked  at  the  previous  milking, 
and  it  is  claimed  that  the  first  few  streams  of  every  milk- 
ing have  a  similar  taste.  In  these  cases  it  is  thought  that 
the  abnormal  taste  is  due  to  bacteria  which  enter  the  teat 
canal.  Certain  staphylococci  and  streptococci  and  some 

66 


MILK  DEFECTS  67 

bacteria  of  the  coli-aerogenes  group  give  milk  a  cow-like, 
salty  taste  (Weigmann). 

2.  "  Fishy  "  Milk. — Milk  from  cows  near  the  end  of 
lactation  may  have  a  "  fishy  "  taste.    This  defect  is  be- 
lieved to  result  also  from  feeding  fish  meal  and  from  graz- 
ing cows  on  marshes  subject  to  overflow  with  salt  water; 
but  cows  have  been  fed  on  large  quantities  of  fish  meal 
without  affecting  the  taste  of  the  milk  or  butter.    In  one 
instance,  the  milk  of  one  cow  in  a  herd  had  such  a  pro- 
nounced "  fishy  "  taste  that  it  tainted  the  milk  from  the 
entire  herd,  although  this  cow  was  fed  and  stabled  in 
exactly  the  same  manner  as  the  others.    The  cause  in  this 
case  could  not  be  determined.     Milk  may  acquire  a 
"  fishy  "  taste  from  milk  vessels  which  are  rusted  and 
also  from  those  which  have  not  been  rinsed  clean  of  the 
soap  powder  used  in  washing  them. 

3.  Rancid  Milk. — A  rancid  odor  and  taste  in  milk  as 
it  comes  from  the  udder  may  be  due  to  the  same  condi- 
tions which  give  milk  a  cow-like  taste.    A  rancid  odor  and 
taste  may  appear  a  short  time  after  the  milk  is  drawn 
from  the  udder  as  a  result  of  the  growth  of  butyric  acid 
bacteria  (page  57).    On  several  occasions  an  unidenti- 
fied biscuit-shaped  organism,  growing  in  pairs,  with  the 
flat  sides  toward  each  other,  has  been  found  to  be  the 
cause  of  a  rancid  odor  and  taste. 

4s.  Slow-creaming  Milk. — The  milk  is  thicker  and 
more  viscous  than  usual;  the  cream  separates  slowly  and 
in  less  quantity  than  normal,  sours  slowly  and  does  not 
"  butter  "  readily.  This  defect  has  been  observed  in  the 
milk  from  cows  near  the  end  of  lactation  and  in  milk  from 
cows  fed  on  beets,  carrots,  and  turnips.  Certain  species 
of  bacteria  greatly  increase  the  viscosity  of  milk,  pro- 


68          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

ducing  what  is  known  as  viscid,  "  ropy,"  or  "  stringy  " 
milk  (page  69). 

5.  Premature  curdling  may  occur  in  connection  with 
disturbances  of  digestion,  udder  diseases,  advanced  preg- 
nancy, overexertion  and  feeding  sour  brewers'  grains 
and  distillery  slop ;  it  may  also  result  from  the  develop- 
ment of  excessive  numbers  of  the  acid-forming  and 
peptonizing  udder  cocci  as  a  consequence  of  incomplete 
milking.    In  the  latter  case,  sodium  bicarbonate  or  sali- 
cylic acid  internally  is  recommended. 

6.  "Gritty"  or  "Sandy"  Milk.— Small  granular 
particles,  concrements  of  calcium  and  magnesium  phos- 
phate, occur  in  milk  when  defects  exist  in  the  epithelium 
of  the  alveoli  of  the  udder  which  permit  the  passage  of 
the  salts  of  the  blood ;  also  when  salts  are  present  in  the 
blood  in  excessive  quantity  as  a  result  of  the  feeding  of 
substances  containing  a  high  percentage  of  mineral  mat- 
ter (Weigmann).    These  granules  may  be  increased  in 
size  by  the  adhesion  of  mucus,  epithelial  cells,  salts,  etc., 
and  form  milk  stones  or  udder  stones  (calculi),  which 
may  make  milking  difficult  or  painful.    The  calculi  are 
of  various  shapes  and  sizes  and  may  be  as  large  as  a  bean. 

"  Bloody  "  milk,  the  ce  flaky  "  milk  occurring  in  mas- 
titis and  the  other  changes  associated  with  disease  of  the 
udder  and  other  pathological  conditions  are  considered 
in  the  chapter  on  the  "  Influence  of  Disease  Upon  Milk." 
For  other  defects,  see  also  the  remarks  under  odor  and 
taste  (page  28). 

(6)  Milk  Defects  which  Appear  after  the  Milk  is  Drawn 
from  the  Udder. — The  greater  part  of  these  defects 
are  caused  by  certain  species  of  bacteria,  yeasts  and 
fungi  which  grow  well  at  low  temperatures.  Spring- 
houses,  cooling-rooms  and  other  dark,  damp  places  fur- 


MILK  DEFECTS  69 

nish  an  environment  favorable  to  their  development. 
Measures  for  the  correction  of  these  defects  must  be 
based  upon  the  source  of  the  organisms  concerned. 

1.  Bitter  Milk. — Several  species  of  bacteria,  yeasts 
and  fungi  have  been  isolated  at  different  times  from  bitter 
milk.    In  some  instances  the  organisms  responsible  for 
the  bitter  taste  were  found  in  the  udder.    Milk  may  ac- 
quire a  bitter  taste  from  the  action  of  the  organisms 
belonging  to  the  peptonizing  and  gas-forming  groups  of 
the  common  milk  bacteria.     This  is  especially  true  of 
heated  milk,  in  which  the  spores  of  the  soil  bacteria  (hay 
and  potato  bacilli  )  survive.    The  occurrence  of  a  bitter 
taste  in  milk  is  often  associated  with  the  feeding  of  cer- 
tain substances,  notably  mouldy  or  decomposed  fodder, 
beet  and  turnip  leaves,  and  raw  potatoes ;  also  vetch,  wild 
mustard  and  other  cruciferous  plants,  leek,  dog-fennel, 
tansy,  etc.    The  use  of  mouldy  or  decomposed  straw  for 
bedding  is  accompanied  by  the  same  effect.    It  is  believed 
that  the  bitter  taste  is  caused  by  organisms  which  are 
present  on  these  substances  and  which  enter  the  milk 
after  it  is  drawn  from  the  udder,  and  it  is  recommended, 
therefore,  that  these  feeds  be  given  after  milking,  except- 
ing, of  course,  those  which  are  mouldy  or  decomposed. 
Another  theory  is  that  the  taste  is  due  to  a  bitter  sub- 
stance which  is  ingested  with  the  food  and  eliminated 
through  the  udder.     If  milk  is  stored  in  rusted  vessels 
until  a  certain  degree  of  acidity  develops,  it  acquires  a 
bitter,  astringent  taste,  due  to  formation  of  iron  lactate 
or  acetate.    Milk  may  also  have  a  bitter  taste  just  before 
parturition  and  near  the  end  of  lactation. 

2.  Viscid, ec Ropy"  or  " Stringy, "  Milk.— The  milk 
is  thick  and  viscid  and  when  it  is  poured  from  one  vessel 
to  another  strings  are  formed ;  it  may  also  be  drawn  out 


70          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

into  long  strings  with  a  rod  or  stick.  The  bacteria  which 
cause  this  defect  are  frequently  introduced  into  the  milk 
by  the  water  used  to  wash  the  milk  vessels  and  utensils. 
Milk-houses,  storage  tanks,  etc.,  may  be  infected  by  the 
same  means.  Water  from  streams  and  shallow  wells 
receiving  surface  drainage,  also  from  springs  receiving 
surface  or  subsurface  drainage,  is  especially  likely  to 
contain  the  organisms.  They  are  also  to  be  found  on 
vegetation  growing  in  low,  damp  places  and  on  straw 
stored  in  a  damp  condition.  In  Sweden  "  stringy  "  milk 
is  prepared  artificially  and  is  a  popular  article  of  food 
(tatmjolk),  while,  in  Holland,  Edam  cheese  is  made 
from  "  stringy  "  milk  produced  by  a  certain  organism. 

3.  fc  Soapy  "  Taste. — Milk  may  acquire  a  "  soapy  " 
taste  from  the  action  of  bacteria  which  attack  the  proteids 
and  fat  of  milk.    Several  species  of  these  organisms  have 
been  found  on  straw  and  fodder. 

4.  Failure  to  Sour  and  "Butter" — Milk  may  not 
sour  and  cream  may  not  sour  and  "  butter  "  at  all  or  only 
very  slowly.    This  defect  may  be  due  to  a  deficiency  in 
acid-forming  bacteria  or  to  an  excess  of  peptonizers.    In 
the  latter  case,  the  milk  or  cream  usually  has  a  bitter 
taste ;  occasionally  a  "  soapy  "  taste.    Alkali-forming  bac- 
teria, butyric  acid  bacteria,  some  of  the  organisms  of  the 
coli-aerogenes  group  and  certain  yeasts  and  fungi  may 
also  delay  or  prevent  souring  and  "  buttering."    In  some 
cases  the  cream  foams  when  churned,  in  consequence  of 
the  formation  of  gas.    This  defect  is  especially  liable  to 
occur  when  cows  are  pastured  on  low,  wet  land;  also  when 
the  leaves  of  roots  (beets,  etc.) ,  are  fed,  and  in  cold,  wet 
weather.    Cream  from  the  milk  of  cows  near  the  end  of 
lactation  will  not  "  butter  "  sometimes  because  of  the 
alkalinity  of  the  secretion. 


MILK  DEFECTS  71 

5.  Stable-like,  turnip-like,  and  beet-like  tastes,  and  a 
burnt  or  malt-like  taste  and  odor  are  each  caused  by  cer- 
tain species  of  bacteria. 

6.  Blue  Milk. — The  Bacillus  cyanogenus,  also  called 
the  Bacterium  syncyaneum,  produces  a  grayish  color  on 
the  surface  of  milk  and,  when  the  milk  is  sour,  blue  spots, 
which  may  become  confluent.    There  are  several  other 
species  of  bacteria  which  produce  a  blue  color  in  milk. 

7.  Red  Milk. — Red  spots  or  a  diffuse  red  color  on  the 
surface  are  produced  by  the  Bacillus  prodigiosus,  also  by 
Sarcina  rosacea  and  several  other  species  of  organisms. 
The  Bacterium  lactis  erythrogenis  curdles  milk,  then 
dissolves  the  curd  and  colors  the  fluid  diffusely  red. 

8.  Yellow-  or  orange-colored  spots  are  produced 
usually  by  the  Bacillus  synxanihus;  also  by  the  Sarcina 
lutea,  Sarcina  ftava  and  the  Bacterium  fulvum. 

9.  A  yellowish-green  discoloration  is  produced  by  the 
Bacillus  pyocyaneus. 

10.  Greenish-yellow  spots  and  diffuse  discoloration 
may  occur  in  sour  milk  as  a  result  of  the  growth  of  the 
Bacillus  ftuorescens. 

11.  Violet-colored  spots  are  produced  by  the  Bacillus 
violaceus,  Bacterium  janihinum,  Bacillus  lividus  and 
Bacterium  amethystinus. 

In  some  cases,  although  very  rarely,  these  pigment- 
forming  bacteria  are  present  in  the  udder.  Usually,  they 
enter  the  milk  after  it  is  drawn  from  the  udder.  They 
can  generally  be  excluded  by  sterilizing  the  milk  vessels 
and  cleaning  and  disinfecting  the  places  where  the  milk 
is  stored;  sunning  it  also  if  possible.  Sometimes  it  will 
also  be  necessary  to  clean  and  disinfect  the  stable  and  to 
see  that  the  cows  are  thoroughly  cleaned  before  milking. 


CHAPTER  VI 

INFLUENCE  OF  DISEASE  UPQN  MILK 

MAN  is  susceptible  to  several  of  the  specific  infectious 
diseases  of  cattle  viz:  tuberculosis,  aphthous  fever  or 
foot  and  mouth  disease,  cowpox,  anthrax,  rabies,  and 
actinomycosis.  Furthermore,  mastitis,  calf  cholera,  acute 
croupous  and  hemorrhagic  enteritis  (paracoli  infection), 
septic  metritis,  and  many  suppurative  conditions  in  cattle 
are  caused  by  bacteria  which  are  pathogenic  for  man.  In 
certain  non-bacterial  affections,  such  as  gastro-intestinal 
catarrh,  the  milk  sometimes  becomes  unpalatable  and, 
when  ingested,  may  cause  irritation  of  the  gastro-intes- 
tinal tract,  especially  in  children. 

The  study  of  the  conditions  under  which  disease-pro- 
ducing organisms  enter  the  milk  and  the  effect  of  disease 
upon  the  milk  secretion  is  one  of  the  important  divisions 
of  milk  hygiene.  Bacteria  or  virus  may  be  carried  by  the 
blood  to  the  udder  and  be  eliminated  with  the  milk,  or 
they  may  be  excreted  through  one  of  the  other  normal 
open  channels  or  discharged  from  wounds  and  enter  the 
milk  after  it  is  drawn  from  the  udder.  The  first  method 
is  called  direct  infection  and  the  latter  secondary  infec- 
tion. There  is  no  doubt  that  bacteria  circulating  in  the 
blood  may  pass  over  into  the  milk  when  the  tissue  sepa- 
rating the  udder  alveoli  and  tubules  from  the  capillaries 
is  broken  down  by  disease.  Some  investigators  are  of 
the  opinion  that  this  may  also  occur  when  the  udder  tissue 
is  intact,  but  this  view  is  disputed  by  others.  When 
bacteria  invade  the  udder  through  the  teat  canal,  as 

72 


INFLUENCE  OF  DISEASE  UPON  MILK  73 

occurs  in  the  non-tuberculous  forms  of  mastitis,  they 
are,  of  course,  always  eliminated  in  the  milk. 

In  considering  the  influence  of  disease  of  the  cow  on 
market  milk,  the  effect  of  dilution  must  not  be  overlooked. 
Milk  from  a  diseased  cow  may  be  injurious  when  ingested 
by  itself,  but  when  it  is  mixed  with  the  milk  from  a  num- 
ber of  other  cows  in  a  normal  condition  it  may  be 
so  diluted  as  to  render  it  harmless.  The  character  of  the 
mixed  milk  in  this  respect  will  depend  partly  upon  the 
proportion  of  diseased  cows  to  those  in  health,  partly 
upon  the  ability  of  the  organism  concerned  to  grow  in 
milk,  and  the  temperature  at  which  the  milk  is  kept. 

The  diseased  conditions  affecting  milch  cows  which 
are  of  importance  in  milk  hygiene  will  now  be  considered 
separately. 

I.  DISEASES  or  CATTLE  TRANSMISSIBLE  TO  MAN 
THROUGH  MILK 

TUBERCULOSIS 

In  milk  hygiene  there  are  four  points  to  be  considered 
in  connection  with  tuberculosis:  (1)  The  frequency  of 
tubercle  bacilli  in  market  milk,  (2)  the  virulence  for 
man  of  tubercle  bacilli  from  cattle,  (3)  the  conditions 
under  which  milk  is  infected  with  tubercle  bacilli  by 
tuberculous  cows,  and  (4)  how  can  contamination  of 
market  milk  with  tubercle  bacilli  be  prevented. 

1.  The  Frequency  of  Tubercle  Bacilli  in  Market  Milk.— 
In  a  number  of  cities  in  this  country  and  abroad,  samples 
of  market  milk  have  been  collected  and  examined  for 
tubercle  bacilli.  Anderson1  examined  233  samples  in 
Washington  in  1906  and  found  tubercle  bacilli  in  6.72 

1  U.  S.  Hygienic  Lab.  Bull.,  No.  56,  pp.  167-197. 


74  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

per  cent.  In  Philadelphia,  in  1908,  Campbell 2  examined 
130  samples  of  raw  milk  and  found  tubercle  bacilli  in 
13.8  per  cent. ;  twelve  samples  of  milk  sold  as  "  pasteur- 
ized "  were  also  examined  by  him  and  one  sample,  or  8.3 
per  cent.,  contained  virulent  tubercle  bacilli.  Hess  3 
found  tubercle  bacilli  in  16  per  cent,  of  the  samples  he 
examined  in  New  York  in  1909,  and  of  144  samples  ex- 
amined by  Tonney  in  Chicago  in  1910  10.5  per  cent,  were 
infected  with  tubercle  bacilli.  In  Germany,  from  16.5 
to  27.1  per  cent,  of  the  samples  of  market  milk  examined 
in  various  cities  contained  tubercle  bacilli;  in  England, 
10  to  25  per  cent. ;  in  Paris,  20  per  cent.,  and  in  Copen- 
hagen, 4  per  cent.4  Another  evidence  of  the  frequency 
of  tubercle  bacilli  in  milk  is  the  general  virulence  of  sep- 
arator milk  from  creameries.  This  milk  has  been  found 
to  be  such  a  great  factor  in  the  dissemination  of  tubercu- 
losis among  calves  and  hogs  that  several  states,  among 
them  Pennsylvania,  have  passed  laws  requiring  such  milk 
to  be  pasteurized  before  it  is  removed  from  the  creamery 
to  be  fed  to  cattle  or  swine. 

There  are  no  statistics  which  show  definitely  the  ex- 
tent to  which  tuberculosis  exists  among  dairy  cattle  in 
the  United  States.  The  disease  is  found  in  less  than  1 
per  cent,  of  the  cattle  slaughtered  for  meat  under  Federal 
inspection,  but  the  greater  proportion  of  these  are  beef 
cattle  and  many  of  them  are  of  young  age,  a  period  when 
tuberculosis  is  not  as  frequently  found  as  in  later  life. 
The  proportion  of  dairy  cows  affected  with  tuberculosis 
is  not  known.  The  per  cent,  of  infected  animals  varies 

2  26th  Annual  Report,  B.  A.  I.,  pp.  175-177. 

3  The  Incidence  of  Tubercle  Bacilli  in  New  York  City  Milk, 
Jour.  Am.  Med.  Assoc.,  No.  13,  Vol.  52. 

4  Rievel,  Milchkunde,  pp.  99-100. 


INFLUENCE  OF  DISEASE  UPON  MILK  75 

greatly  in  different  localities  and  in  different  herds 
in  the  same  section.  The  proportion  of  animals  reacting 
to  the  tuberculin  test  ranges  from  none  in  herds  which 
have  been  subjected  to  annual  tests  for  several  years  to 
30  per  cent,  and  over  in  herds  in  which  no  effort  has  been 
made  to  control  the  disease. 

2.  Virulence  for  Man  of  Tubercle  Bacilli  from  Cattle.—- 
— Until  1901  it  was  very  generally  accepted  that  tuber- 
culosis in  man  and  animals  was  the  same  disease,  although 
Theobold  Smith,  in  1896,  and,  subsequently,  others, 
pointed  out  important  differences  in  virulence,  morphol- 
ogy, and  cultural  characteristics  between  bacilli  from 
human  and  bovine  sources.  In  1901  Koch  announced 
that  tuberculosis  of  cattle  was  so  rarely  transmitted  to 
man  that  it  could  practically  be  disregarded  in  formulat- 
ing plans  to  protect  man  against  the  disease.  This  an- 
nouncement was  based  on  the  failure  of  Koch  and  Schiitz 
to  infect  calves  and  other  animals  with  tuberculous  ma- 
terial from  man,  and  upon  post-mortem  statistics  col- 
lected by  them  of  a  number  of  cases  of  tuberculosis  in  man 
which  happened  to  include  only  a  small  proportion  of  in- 
dividuals showing  primary  lesions  in  the  digestive  tract 
or  attached  lymph  glands.  Koch's  announcement  made 
a  pronounced  impression  upon  the  general  public,  al- 
though his  experiments  were  not  original  nor  were  his  re- 
sults undisputed.  Theobold  Smith,  Frothingham,  and 
Dinwiddie  in  this  country,  and  Piitz,  Gaiser,  Nbcard, 
McFadyean,  Thomasson,  Chauveau,  Klebbs,  Kitt,  Bol- 
linger,  and  Crookshank  abroad,  had  previously  at- 
tempted to  infect  cattle  with  tuberculous  material  from 
man  and  had  succeeded  in  doing  so,  although  they  found 
that  these  animals  were  less  susceptible  to  human  tuber- 
culous material  than  to  that  from  bovine  sources.  Since 


76  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Koch's  announcement  was  made,  some  thirty-five  or  forty 
investigators  in  different  parts  of  the  world  have  at- 
tempted to  transmit  human  tuberculosis  to  cattle  and 
all  have  succeeded  but  one. 

As  to  the  other  point  upon  which  Koch  based  his  views, 
the  frequency  of  primary  tuberculosis  of  the  digestive 
tract  or  attached  lymph  glands,  we  learn  from  the  in- 
vestigations of  others  that,  while  this  form  of  tuberculosis 
is  rare  in  adults,  the  proportion  of  cases  found  in  children 
by  different  investigators  is  extremely  variable,  ranging 
from  %  to  37.8  per  cent. ;  consequently  the  statistics  col- 
lected by  any  one  or  two  men  cannot  be  accepted  as 
representing  the  percentage  of  cases  in  which  the  lesions 
are  primary  in  the  digestive  tract  or  attached  lymph 
glands.  Evidence  has  also  been  produced  by  the  experi- 
ments of  Mohler,  Ravenel,  Calmette,  and  others  that 
tubercle  bacilli  may  be  introduced  through  the  digestive 
tract  and  primary  lesions  established  in  the  lungs  or 
thoracic  lymph  glands  without  producing  any  lesions  in 
the  intestines  or  mesenteric  lymph  glands. 

Koch's  views  were  not  accepted  by  many  of  those  who 
had  made  a  special  study  of  tuberculosis,  and  his  an- 
nouncement instigated  a  vast  amount  of  research  work. 
Commissions  were  appointed  by  the  British  and  German 
governments  to  investigate  the  relation  of  bovine  to 
human  tuberculosis,  and  other  official  bodies,  and  many 
individuals  also  took  up  the  study  of  the  subject.  Koch 
contended  that  it  could  be  assumed  that  tKe  infecting 
material  had  been  ingested  with  the  food  only  when 
primary  lesions  were  found  in  the  digestive  tract  or  its 
attached  lymph  glands,  and  that  only  those  cases  in  which 
tubercle  bacilli  of  the  bovine  type  were  demonstrated  in 
the  lesions  could  be  regarded  as  having  been  infected  by 


INFLUENCE  OF  DISEASE  UPON  MILK  77 

the  products  (meat  and  milk)  of  tuberculous  animals. 
The  investigations  were  therefore  largely  directed  along 
these  lines.  The  present  views  of  those  who  have  studied 
the  subject  are  fairly  represented  by  the  conclusions 
reached  by  the  British  commission  and  published  in  1911 
after  a  careful  and  thorough  inquiry  extending  over  ten 
years.  These  conclusions  are  as  follows: 

"  There  can  be  no  doubt  that  a  considerable  propor- 
tion of  the  tuberculosis  affecting  children  is  of  bovine 
origin,  more  particularly  that  which  affects  primarily  the 
abdominal  organs  and  the  cervical  glands.  !And,  fur- 
ther, there  can  be  no  doubt  that  primary  abdominal  tuber- 
culosis as  well  as  tuberculosis  of  the  cervical  glands  is 
commonly  due  to  ingestion  of  tuberculous  infective 
material."  One  hundred  and  eight  cases  of  human  tuber- 
culosis other  than  lupus  were  examined  by  the  Commis- 
sion and  bacilli  of  the  bovine  type  were  found  in  twenty- 
four,  or  22  per  cent.  The  latter  included  sixteen  cases 
of  primary  abdominal  tuberculosis,  three  of  tuberculosis 
of  the  cervical  lymph  glands,  two  of  pulmonary  tubercu- 
losis, two  of  tuberculosis  of  the  bronchial  lymph  glands 
and  one  of  joint  tuberculosis.  Bacilli  of  the  bovine  type 
were  found  in  nearly  half  of  the  fatal  cases  of  primary 
abdominal  tuberculosis. 

The  German  commission  made  a  study  of  fifty-six 
different  cultures  obtained  from  cases  of  tuberculosis  in 
man  and  found  six,  or  more  than  10  per  cent.,  to  be  of 
the  bovine  type. 

Park  and  Krumwiede 5  determined  the  type  of  bacilli 
present  in  487  cases  of  tuberculosis  in  man  and  collected 
from  the  literature  the  records  of  1033  cases  in  which  the 

5  Journal  Med.  Research,  pp.  109-114,  vol.  27. 


78  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

type  of  the  organism  was  determined  by  others,  a  total  of 
1511  cases.  There  were  955  cases  in  individuals  over  16 
years  of  age,  177  in  children  between  5  and  16  years,  and 
368  in  children  under  5.  Tubercle  bacilli  of  the  bovine 
type  were  found  in  35  per  cent,  of  the  cases  in  children 
between  the  ages  of  5  and  16,  and  in  26  per  cent,  of  the 
cases  in  children  under  5.  In  addition  to  these,  there  were 
eleven  cases  in  which  both  types  of  bacilli  were  found. 

It  is  usually  difficult  to  discover  the  source  of  infec- 
tion in  cases  of  tuberculosis  in  man  because  the  disease 
does  not  become  apparent  for  a  long  time  after  exposure 
to  infection  has  occurred.  Nevertheless,  there  are  a 
number  of  cases  recorded  of  tuberculosis  in  children  and 
adults  using  milk  from  tuberculous  cows  for  which  no 
other  source  of  infection  could  be  found.6  Regarding  the 
evidence  in  these  cases  as  generally  incomplete,  Koch,  in 
1902,  suggested  that  a  search  be  made  for  cows  in  which 
tuberculosis  of  the  udder  could  be  positively  diagnosed 
and,  when  such  cases  were  found,  that  it  be  ascertained 
how  long  the  disease  had  existed,  who  consumed  the  milk 
or  its  products,  whether  the  milk  was  used  raw  or  cooked, 
and  if  the  persons  who  used  the  milk  or  its  products  were 
infected  with  tuberculosis.  Between  1905  and  1909 
Weber  and  Ungerman7  found  in  Germany  69  cases  of 
udder  tuberculosis  concerning  which  the  information  de- 
sired could  be  obtained.  Three  hundred  and  sixty  per- 
sons, including  151  children,  used  milk  from  these  cows. 
Two  boys  were  affected  with  tuberculosis  of  the  cervical 
lymph  glands  in  which  bacilli  of  the  bovine  type  were 

6  Rievel,  Milchkunde,  pp.  107-108. 

7  Cited  by  Ostertag,  Zeitschr.  fur  Fleisch  u.  MilcKhygiene, 
pp.  26  and  27,  No.  2,  vol.  xxiii ;  p.  123,  No.  6,  vol.  xxiv. 


INFLUENCE  OF  DISEASE  UPON  MILK  79 

demonstrated.  Six  other  children  and  one  adult  were 
found  with  swelling  of  the  cervical  lymph  glands,  four 
children  and  one  adult  showed  symptoms  indicative  of 
abdominal  tuberculosis  and  one  child  suffered  from 
scrofula,  but  in  these  cases  no  material  could  be  obtained 
for  bacteriological  examination.  Forty-one  other  persons 
showed  various  symptoms  of  disease,  but  tubercle  bacilli 
could  be  demonstrated  in  only  4,  and  these  bacilli  were  of 
the  human  type.  The  other  304  individuals  who  had  used 
milk  from  the  tuberculous  udders,  or  products  made  from 
such  milk,  showed  no  symptoms  of  disturbed  health  in 
1910.  Subsequently,  one  of  these,  a  girl,  developed  a 
peritonitis  for  which  the  infected  milk  was  probably  re- 
sponsible. While  in  some  instances  the  milk  was  heated, 
mixed  with  milk  from  apparently  healthy  cows,  or  only 
a  small  quantity  was  used  in  tea  or  coffee,  nevertheless  the 
results  of  this  investigation  would  indicate  that  a  con- 
siderable amount  of  infectious  material  and  favorable 
accessory  conditions  are  required  to  infect  man  with 
bovine  tuberculosis.  But,  as  Weber  himself  has  pointed 
out,  it  must  be  remembered  that  it  is  not  known  positively 
that  the  individuals  manifesting  symptoms  suspicious  of 
cervical  lymph  gland  and  abdominal  tuberculosis  were 
not  actually  infected,  nor  how  many  of  the  apparently 
healthy  persons  concerned  were  affected  with  lat- 
ent tuberculosis  which  may  later,  under  some  debilitat- 
ing influence,  become  active  and  progress  to  a  fatal 
termination. 

Furthermore,  Weber's  observations  are  not  confirmed 
by  others  who  have  studied  the  frequency  of  the  trans- 
mission of  bovine  infection  to  man  by  milk.  A.  comparison 
of  the  occurrence  of  tuberculosis  in  breast-fed  children 


80  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

with  the  frequency  of  the  disease  in  children  receiving 
cow's  milk  was  made  by  Sobotta.  Of  80  exclusively 
breast-fed  children,  17.5  per  cent,  were  infected  with 
tuberculosis ;  of  57  children  receiving  cow's  milk  in  addi- 
tion to  mother's  milk,  35.1  per  cent,  were  infected,  and 
of  30  fed  exclusively  on  cow's  milk  41  per  cent,  became 
tuberculous.8  Mitchell 9  examined  72  cases  of  cervical 
gland  tuberculosis  in  the  Children's  Hospital  in  Edin- 
burgh and  found  tubercle  bacilli  of  the  bovine  type  in 
65,  or  90  per  cent.  These  children  came  from  districts 
in  which  the  cattle  are  extensively  infected  with  tuber- 
culosis and  most  of  them  had  been  nourished  on  cow's 
milk.  Of  70  cases  of  tuberculosis  of  the  bones  and  joints 
in  children  examined  by  Fraser  9  in  Edinburgh,  41,  or 
60  per  cent.,  were  due  to  bacilli  of  the  bovine  type  and  in 
the  greater  number  of  cases  the  history  indicated  that  the 
infection  was  introduced  by  cow's  milk.  In  261  cases  of 
bone  and  joint  disease  examined  by  Eastwood  and 
Griffith,10  bacilli  of  the  bovine  type  were  found  in  55,  or 
21.1  per  cent.  Of  these  latter,  29  per  cent,  were  from 
patients  under  10  years  of  age  and  9.4  from  patients 
over  that  age.  Seventeen  cases  of  genito-urinary  dis- 
eases were  examined.  Bacilli  of  the  bovine  type  were 
found  in  three  cases  of  kidney  disease  in  persons  25,  19 
and  20  years  old,  respectively.  Twelve  and  one-half  per 
cent,  of  the  fatal  cases  of  tuberculosis  in  children  under 
5  years  old  studied  by  Park  and  Krumweide  n  were 

8  Cited  by  Rievel,  Milchkunde,  p.  110. 

9  Cited  by  Ostertag,  Zeitschr.  fur  Fleisch  u.  Milchhygiene, 
p.  69,  No.  3,  vol.  24;  p.  118,  No.  5.  vol.  24. 

10  Journal  of  Hygiene,  pp.  257-309,  310-314,  No.  2,  vol.  15. 

11  Jour.  Med.  Research,  pp.  109-114,  vol.  27. 


INFLUENCE  OF  DISEASE  UPON  MILK  81 

due  to  bovine  infection.  They  had  nine  cases  in  a  found- 
ling asylum  in  children  under  6  years  who  were  nourished 
exclusively  on  cow's  milk  and  found  bovine  infection  in 
five,  or  over  50  per  cent.  Of  the  fatal  cases  in  the  Babies' 
Hospital  in  New  York  City  6%  per  cent,  were  due  to 
bovine  infection. 

These  observations  cannot  be  ignored  in  considering 
the  results  of  Weber  and  Ungermann's  investigation, 
especially  since  they  all  indicate  that  bovine  tuberculosis 
is  a  considerable  source  of  infection  for  children  and  are 
also  in  accord  with  the  results  of  other  studies  of  the 
disease. 

3.  Conditions  under  which  Milk  is  Infected  with  Tubercle 
Bacilli  by  Tuberculous  Cows.— The  milk  of  individual  cows 
affected  with  tuberculosis  in  various  forms  has  been 
tested  for  the  presence  of  tubercle  bacilli  by  injecting 
it  into  guinea  pigs  and  by  feeding  it  to  these  animals. 
Numerous  experiments  of  this  kind  have  been  conducted, 
and  upon  the  basis  of  these  experiments  tuberculous  cows 
may  be  divided  into  three  classes  as  regards  the  infectious- 
ness  in  their  milk,  viz:  (a)  Cows  affected  with  tubercu- 
losis of  the  udder;  (b)  cows  with  apparently  normal 
udders  but  showing  clinical  symptoms  in  other  organs  or 
parts,  and  (c)  cows  which  do  not  show  any  clinical  symp- 
toms but  which  have  reacted  to  the  tuberculin  test. 

(a)  Cows  Affected  with  Tuberculosis  of  the  Udder. 
— When  the  udder  is  tuberculous,  tubercle  bacilli  are 
eliminated  in  the  milk.  In  advanced  or  extensive  cases 
of  this  form  of  the  disease,  the  milk  is  very  infectious ;  it 
contains  from  50,000  to  100,000  and  even  1,000,000 
tubercle  bacilli  per  c.c.  (Ostermann),  and  remains  viru- 
lent when  injected  into  guinea  pigs  after  it  has  been 
6 


82  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

diluted  one  billion  times  (Ostertag).12  In  the  initial 
stages,  when  the  tuberculous  areas  in  the  udder  are  small 
and  isolated,  the  tubercle  bacilli  are  less  numerous,  num- 
bering about  1000  per  c.c.  While  such  milk  must  be 
diluted  about  1000  times  to  render  it  non- virulent  when 
injected  into  guinea  pigs,  it  may  be  repeatedly  fed  to 
them  undiluted  without  producing  tuberculosis. 

As  to  the  frequency  of  tuberculosis  of  the  udder,  in 
the  post-mortem  examination  of  1200  cattle  reacting  to 
the  tuberculin  test,  nearly  all  of  which  were  dairy  cows, 
Pearson  found  the  udder  tuberculous  in  104,  or  5.75  per 
cent.  Ostertag  estimates  that  the  disease  is  present  in 
the  udder  of  0.1  to  0.3  per  cent,  of  all  cows.  In  consider- 
ing the  frequency  of  tuberculosis  of  the  udder,  the  large 
number  of  bacilli  present  in  the  milk  in  advanced  cases 
must  be  remembered.  The  milk  of  one  cow  affected  with 
advanced  or  extensive  tuberculosis  of  the  udder  can  infect 
thousands  of  quarts  of  milk  from  other  cows,  if  mixed 
with  it,  and  may  even  render  the  entire  supply  of  a 
small  town  infectious. 

(b)  Cows  with  Apparently  Normal  Udders  but 
Showing  Clinical  Symptoms  in  Other  Organs  or  Parts. — 
Milk  from  cows  in  this  condition  frequently  contains 
tubercle  bacilli.  It  appears  very  probable  that  the  udder 
is  actually  diseased  when  tubercle  bacilli  are  eliminated 
in  the  milk  of  such  cows.  The  udder  may  be  tuberculous 
and  yet  be  apparently  normal.  The  disease  is  always 
extensive  when  clinical  symptoms  are  present,  and 
usually  it  is  generalized — tubercle  bacilli  have  repeatedly 
invaded  the  blood  stream  and  have  had  abundant  oppor- 

12  Zeitschr  fur  Fleisch  u.  Milchhy.,  pp.  26  and  27,  No.  2, 
vol.  xxiii. 


INFLUENCE  OF  DISEASE  UPON  MILK  83 

tunity  to  locate  in  the  udder  and  to  produce  small,  fresh 
tubercles,  too  small  to  be  discovered  by  palpation  of  the 
udder.  Such  lesions  may  even  escape  observation  on 
post-mortem  examination  because  of  their  similarity  in 
appearance  to  the  actively  secreting  udder  tissue.  Rick 
found  the  udder  tuberculous  in  17.6  per  cent,  of  the  cases 
of  generalized  tuberculosis  examined  by  him.  Joest  and 
Kracht 13  found  the  supramammary  lymph  glands  tuber- 
culous, when  tested  by  inoculation,  in  50  per  cent,  of  the 
cases  examined  by  them  of  generalized  tuberculosis  in 
which  the  udder  did  not  show  any  clinical  symptoms  or 
macroscopic  lesions  on  post-mortem  examination;  some 
of  the  lymph  glands  were  slightly  enlarged  but  otherwise 
they  were  of  normal  appearance.  In  one-half  of  these 
cases  the  udder  tissue  was  also  infected.  It  would  there- 
fore appear  that  the  udder  is  much  more  frequently  tuber- 
culous in  cases  of  generalized  tuberculosis  than  is  gener- 
ally suspected. 

Contradictory  views  exist  as  to  the  possibility  of 
tubercle  bacilli  passing  through  the  sound  udder.  Oster- 
tag  and  Prettner  injected  tubercle  bacilli  intravenously 
into  cows  with  sound  udders  and  found  the  milk  non- 
virulent  when  inoculated  into  guinea  pigs. 

Milk  may  be  infected  secondarily  with  tubercle  bacilli 
when  open  tuberculosis  is  present  in  the  lungs,  intestines, 
or  uterus.  Cows  affected  with  open  tuberculosis  of  the 
lungs  swallow  the  greater  part  of  the  infected  material 
coughed  up,  and  it  passes  out  with  the  fasces;  the  tubercle 
bacilli  are  not  destroyed  by  the  digestive  secretions  and 
remain  virulent.  Schroeder 14  and  the  British  tubercu- 

13  Joest  and  Kracht,  Zeitschr.   fur  Infectionskrank.,   etc., 
pp.  315-316,  vol.  12,  No.  4,  1912. 

14  Schroeder,  p.  120,  25th  Annual  Report  B.  A.  I. 


84  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

losis  commission  found  the  faeces  infectious  from  tuber- 
culous cows  which  did  not  show  any  clinical  symptoms, 
but  these  results  have  not  been  confirmed  by  others. 
Titae,  Thieringer  and  Jahn15  demonstrated  tubercle 
bacilli  in  the  f seces  of  cows  affected  with  open  pulmonary 
tuberculosis,  but  not  in  the  fasces  of  reacting  cows  which 
did  not  show  clinical  symptoms.  Traum16  inoculated 
guinea  pigs  with  fecal  material  from  36  cows,  "  prac- 
tically all  tuberculin  reactors,"  and  none  of  the  guinea 
pigs  was  infected  with  tuberculosis,  although  two  of  the 
cows  exhibited  physical  symptoms  of  disease  of  the  lungs. 
These  results  correspond  with  those  obtained  when 
samples  of  mixed  milk  from  herds  known  to  be  infected 
with  tuberculosis  have  been  examined  for  tubercle  bacilli. 
For  example,  O.  Miiller  examined  samples  of  milk  from 
1598  herds  in  East  Prussia  and  tubercle  bacilli  were 
demonstrated  in  the  samples  from  only  97  herds,  al- 
though non-clinical  reactors  were  present  in  the  other 
herds.  In  the  97  herds  from  which  the  samples  contain- 
ing tubercle  bacilli  were  obtained,  cows  were  found  which 
exhibited  clinical  symptoms  of  udder  tuberculosis  or 
other  forms  of  the  disease.  Similar  results  could  be 
cited.  Reichel 17  found  the  faeces  infectious  from  cows 
which  were  not  tuberculous  but  which  were  stabled  with 
cows  affected  with  open  tuberculosis.  It  therefore  ap- 
pears probable  that  the  sputum  coughed  out  by  cows 
with  open  tuberculosis,  or  the  fine  spray  expelled  from 
the  mouth  in  coughing,  may  contaminate  the  feed  of  other 

15  Arbeit.  K.  Gesundheitsamt,  pp.  1-34,  No.  1,  1913. 

16  Annual  Report  University  of  California  Expt.  Station, 
1915,  p.  40. 

17  Verbal  communication. 


INFLUENCE  OF  DISEASE  UPON  MILK  85 

cows  and  that  these  cows  may  eliminate  virulent  tubercle 
bacilli  in  the  fseces  even  when  they  are  not  infected  with 
tuberculosis.  The  presence  of  the  bacilli  in  the  faeces  of 
tuberculous  cows  without  open  lesions  in  the  lungs  or 
intestines  and  without  disease  of  the  liver  may  be  ex- 
plained on  the  same  basis.  Titze  and  Jahn  found  that 
in  tuberculosis  of  the  liver  virulent  tubercle  bacilli  may 
be  excreted  in  the  bile  and  eliminated  with  the  f  geces,  thus 
confirming  the  earlier  findings  of  Joest  and  Emshoff . 
The  udder  and  posterior  parts  of  the  cows  affected  with 
open  tuberculosis  become  soiled  with  the  infected  faeces 
or  vaginal  discharges,  and  particles  of  this  material  drop 
off  into  the  milk  during  milking,  thus  infecting  the  milk 
secondarily.  The  demonstration  of  tubercle  bacilli  in 
the  milk  of  individual  cows  does  not  therefore  necessarily 
indicate  that  the  bacilli  were  excreted  through  the  udder. 
Milk  from  cows  with  open  tuberculosis  usually  contains 
about  1000  tubercle  bacilli  per  c.c.  While  it  does  not 
always  produce  tuberculosis  when  fed  to  guinea  pigs,  or 
even  when  injected  into  them,  it  is  often  infectious  and 
must  therefore  be  regarded  as  dangerous. 

(c)  Cows  which  do  not  Show  any  Clinical  Symp- 
toms but  which  have  Reacted  to  the  Tuberculin  Test 
(Non-clinical  Reactors). — The  experiments  with  indi- 
vidual milk  from  cows  which  had  reacted  to  the  tuberculin 
test,  but  which  did  not  show  any  clinical  symptoms  of  the 
disease,  have  given  contradictory  results.  Ostertag, 
Brauer,  Ascher,  Miiller,  Stenstrom,  Bassett,  and  others 
have  found  the  milk  from  non-clinical  reactors  to  be  free 
from  tubercle  bacilli,  while  Rabinowitch  and  Kempner, 
Schroeder,  Ravenel,  Mohler,  Martel,  Guerin,  DeJong, 
Moussu,  and  Fay  have  found  tubercle  bacilli  present  in 
milk  from  such  cows.  Ostertag  tested  the  milk  of  49 


86  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

non-clinical  reactors  and  not  a  single  sample  produced 
tuberculosis  when  in  j  ected  into  guinea  pigs.  Later,  in  con- 
j  unction  with  Brauer,18  he  made  a  thorough  test  of  the 
milk  from  10  non-clinical  reactors,  inoculating  guinea 
pigs,  and  feeding  guinea  pigs,  calves  and  pigs.  Not  one 
of  the  experimental  animals  developed  tuberculosis. 
Some  of  the  guinea  pigs  in  the  feeding  experiment  re- 
ceived 66  grammes  of  milk  daily  for  5  months,  or  33  times 
their  body  weight;  10  calves  received  7  to  12  litres  each 
day  for  8  to  11  months  and  20  pigs  were  given  1  to  6 
litres  daily  for  4  months.  O.  Miiller  made  inoculation 
tests  on  guinea  pigs  with  the  milk  from  9  non-clinical 
reactors,  and  Ascher  with  the  milk  from  7,  and  tubercle 
bacilli  were  not  demonstrated  in  a  single  case.  Ostertag 
contends  that  in  those  cases  in  which  tubercle  bacilli  were 
demonstrated  in  the  milk  from  non-clinical  reactors,  the 
milk  was  infected  secondarily,  and  in  support  of  this 
view  he  points  out  that  in  some  of  the  cases  in  which 
tubercle  bacilli  were  demonstrated  in  the  milk  no  lesions 
of  tuberculosis  could  be  found  on  postmortem,  while  in 
other  cases  lesions  of  open  tuberculosis  were  present.  At 
any  rate,  the  evidence  in  its  entirety  indicates  that  the 
milk  of  non-clinical  reactors  is  much  less  likely  to  contain 
tubercle  than  the  milk  of  cows  with  tuberculous  udders 
or  which  show  clinical  symptoms  of  the  disease  in  other 
organs. 

Influence  of  Dilution. — While  these  experimental  re- 
sults indicate  very  accurately  the  conditions  under  which 
tuberculous  cows  contaminate  milk,  it  must  not  be  for- 
gotten that  they  relate  to  the  milk  of  individual  cows 
tested  separately,  while  in  practice  the  milk  of  tuber- 

18  Zeitschr.  fur  Fleisch  u.  Milchhy.,  p.  80,  No.  4,  vol.  xxiv. 


INFLUENCE  OF  DISEASE  UPON  MILK  87 

culous  cows  is  diluted  more  or  less  with  the  milk  of  non- 
infected  cows.  The  extent  of  the  dilution  will  depend 
upon  the  method  of  handling  the  milk.  Ordinary  mar- 
ket milk,  however,  is  frequently  the  mixed  milk  of  sev- 
eral herds,  but  at  any  rate  it  is  the  mixed  milk  of  a  number 
of  cows  in  the  same  herd.  It  has  been  demonstrated  that 
the  milk  of  cows  affected  with  advanced  or  extensive 
tuberculosis  of  the  udder  may  render  the  entire  supply 
infectious  when  mixed  with  milk  from  other  cows  which 
are  not  tuberculous ;  but  this  is  not  true  of  milk  from  cows 
which  do  not  show  clinical  symptoms  of  the  disease. 
Miiller  and  Hessler  examined  by  inoculation  samples 
of  mixed  milk  from  2949  herds,  each  sample  representing 
the  milk  from  30  to  200  cows.  Tubercle  bacilli  were 
present  in  the  samples  from  156  herds.  All  of  these 
herds  except  five  were  found  to  contain  cows  affected 
with  udder  tuberculosis  or  other  forms  of  open  tuber- 
culosis. In  the  five  herds  in  which  tuberculosis  was  not 
established  clinically,  Hessler  is  of  the  opinion  that  the 
tubercle  bacilli  were  eliminated  in  the  fasces  by  cows  with 
incipient  cases  of  open  lung  tuberculosis  which  had  not 
yet  become  perceptible.  The  other  2793  herds,  in  the 
milk  samples  from  which  tubercle  bacilli  were  not  demon- 
strated, certainly  contained  a  considerable  number  of 
cows  which  would  have  reacted  to  the  tuberculin  test, 
judging  from  the  extent  to  which  tuberculosis  was  known 
to  exist  in  the  district  in  which  they  were  located. 

Delepine  examined  the  milk  from  1385  farms  and 
found  tubercle  bacilli  in  the  samples  from  294  farms. 
The  cattle  on  276  of  these  farms  were  examined  and  on 
190  farms  one  or  more  cows  were  found  affected  with 
tuberculosis  of  the  udder,  a  bacteriological  examination 
of  the  individual  milk  being  necessary  in  some  cases  to 


88  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

discover  the  condition.  After  these  cows  were  removed, 
the  milk  from  these  farms  ceased  to  infect  guinea  pigs. 
No  clinical  cases  of  udder  tuberculosis  were  found  in  the 
other  86  herds  examined,  but  on  these  farms  cows  had 
been  sold  between  the  time  the  milk  samples  were  col- 
lected and  the  herd  was  examined,  or  the  farmer  had  been 
buying  milk  from  other  sources  when  the  samples  were 
collected. 

Friis  inoculated  guinea  pigs  with  samples  of  mixed 
milk  from  28  dairy  farms  in  and  about  Copenhagen  and 
demonstrated  tubercle  bacilli  in  the  samples  from  four 
farms.  On  one  of  these  farms  two  cows  with  tuberculosis 
of  the  udder  were  found  and  one  cow  with  udder  tuber- 
culosis was  found  on  another,  while  on  the  other  two 
farms  cows  were  found  showing  physical  symptoms  of 
tuberculosis  in  other  organs.  There  is  no  doubt  that  the 
other  twenty- four  farms  contained  cows  which  would  have 
reacted  to  the  tuberculin  test. 

The  milk  from  12  non-clinical  reactors  was  tested  for 
tubercle  bacilli  by  Klein  and  Campbell  by  injection  into 
guinea  pigs.  These  cows  were  in  a  stable  with  12  other 
non-clinical  reactors  which  were  not  included  in  the  ex- 
periment because  they  were  approaching  the  end  of  the 
lactation  period.  The  stable  was  light,  well- ventilated,  of 
suitable  size  and  clean.  The  cows  were  cleaned  with  a 
curry-comb  and  brush  and  the  udders  wiped  with  a  damp 
cloth  before  each  milking.  All  the  cows  in  the  stable  were 
examined  by  inspection,  palpation  and  auscultation  when 
the  experiment  began  and  no  symptoms  indicating  tuber- 
culosis were  found.  They  were  all  in  a  good,  thrifty 
condition  and  none  had  a  chronic  cough.  (All  suspici- 
ous animals  had  been  previously  removed.)  The  12  cows 
used  in  the  experiment  were  arranged  in  groups  of  three 


INFLUENCE  OF  DISEASE  UPON  MILK  89 

each  according  to  the  stage  of  lactation  and  once  each 
week  the  milk  from  each  group  was  put  into  a  separate 
can,  the  cows  being  groomed  and  milked  in  the  usual 
manner  by  the  regular  attendants.  A  sample  of  milk 
was  taken  from  each  can  for  examination.  Two  guinea 
pigs  were  inoculated  from  each  sample — one  with  the 
cream  and  one  with  the  sediment.  This  was  repeated  each 
week  for  six  weeks.  Then  the  cows  in  the  stable  were 
again  examined  in  the  same  way  and,  no  symptoms  indi- 
cating tuberculosis  being  found,  samples  of  milk  were 
collected  and  examined  as  before  once  a  week  for  another 
period  of  six  weeks.  Altogether,  96  guinea  pigs  were 
inoculated.  Thirty  died  of  intercurrent  disease  and  the 
other  66  were  chloroformed  two  months  after  inoculation. 
A  post-mortem  examination  was  made  of  every  animal, 
but  in  no  instance  were  any  lesions  of  tuberculosis  found. 
One  of  the  cows  in  the  experiment  had  reacted  to  tuber- 
culin over  8  years  before,  one  7  years,  two  6  years,  two  4 
years,  two  3  years,  two  2  years,  one  1  year  and  one  4 
months  before. 

These  observations  show  that  non-clinical  reactors 
play  a  minor  role  in  the  infection  of  market  milk  with 
tubercle  bacilli,  even  when  the  virulence  of  the  milk  is 
tested  by  the  delicate  fnoculation  test.  That  there  is  a 
vast  difference  between  the  number  of  tubercle  bacilli 
necessary  to  produce  infection  by  the  mouth  and  by  in- 
oculation has  been  demonstrated  by  a  number  of  investi- 
gators. Ostertag  and  others  have  shown  that  two  and  a 
half  million  times  more  material  is  required  to  infect  an 
animal  by  feeding  than  by  inoculation.  Schroeder  and 
Cotton  found  that  milk  which  would  produce  tubercu- 
losis in  guinea  pigs  when  5  c.c.  was  injected  into  the 
peritoneal  cavity  could  be  fed  30  days  without  producing 


90          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

the  disease.  Findel,  Reichenbach  and  Alexander19  found 
that  at  least  400,000,000  tubercle  bacilli  are  necessary 
to  produce  infection  when  only  a  single  dose  is  fed  to 
guinea  pigs  and  that  800,000  tubercle  bacilli  given  fifty 
times  by  the  mouth  are  not  certain  to  produce  infection. 
Ostermann20  reports  that  milk  containing  1000  bacilli 
per  c.c.  may  be  repeatedly  ingested  without  effect. 
Fliigge  and  his  co-workers  also  found  that  while  a  very 
few  tubercle  bacilli  are  sufficient  to  produce  a  severe 
tuberculosis  when  injected  into  a  guinea  pig,  200  are 
necessary  when  the  bacilli  are  inhaled  and  140,000,000 
when  they  are  ingested. 

4.  How  can  Contamination  of  Market  Milk  with 
Tubercle  Bacilli  be  Prevented? — The  information  at 
hand  shows  that  cows  with  tuberculosis  of  the  udder  are 
by  far  the  greatest  factors  in  infecting  market  milk  with 
tubercle  bacilli  and  that  next  in  -order  are  those  with  ap- 
parently healthy  udders  but  showing  clinical  symptoms 
of  the  disease  in  other  organs.  Compared  with  these 
two  classes,  cows  which  present  no  evidence  of  tubercu- 
losis except  a  reaction  to  the  tuberculin  test  are  a  rather 
insignificant  source  of  contamination. 

The  contamination  of  milk  with  tubercle  bacilli  can 
be  most  thoroughly  and  most  certainly  prevented  by  re- 
moving from  the  herds  concerned  in  a  milk  supply  the 
cows  belonging  to  all  three  classes.  This  could  only  be 
accomplished  by  making  a  tuberculin  test  and  physical 
examination  and  repeating  them  at  certain  intervals.  A 

19  Cited  by  Ostertag,  Zeitschr.  fur  Fleisch  u.  Milchhy.,  p. 
27,  No.  2,  vol.  xxiii. 

20  Cited  by  Klimmer,  Osterreich.  Wochenschr.  fiir  tierheilk. 
u.  Tierzucht,  No.  45,  1912. 


INFLUENCE  OF  DISEASE  UPON  MILK  91 

physical  examination  in  addition  to  a  tuberculin  test  is 
necessary  because  the  tuberculin  test  alone  will  not  detect 
all  cases  of  tuberculosis.  Ostertag,  for  instance,  tested 
with  tuberculin  nine  cows  affected  with  udder  tubercu- 
losis and  two  failed  to-  react.  The  adoption  of  such  a 
plan,  however,  immediately  upon  the  introduction  of 
dairy  inspection  in  districts  in  which  tuberculosis  is  com- 
mon will  meet  with  many  practical  difficulties.  Few 
dairymen  in  such  districts  are  able  to  bear  the  expense 
of  disposing  of  non-clinical  reactors  as  well  as  clinical 
cases  and  of  replacing  them  with  healthy  cows,  even 
with  state  assistance ;  and  the  state  would  not  have  suffici- 
ent funds  to  render  the  assistance  provided  by  present 
laws  if  such  a  plan  was  generally  adopted.  Difficulty 
would  also  be  experienced  in  replacing  the  reacting  cattle 
with  animals  free  from  tuberculosis,  and  this  would  in- 
crease with  the  number  of  herds  included  in  the  inspection. 
The  opposition  of  the  dairymen  concerned  would  be 
very  generally  incurred  and  there  would  not  exist  that 
friendly  cooperation  between  the  inspector  and  dairy- 
man which  is  necessary  to  insure  the  most  satisfactory 
results.  A  careful  and  thorough  physical  examination 
repeated  at  intervals  is  next  in  the  order  of  effectiveness. 
By  this  method  those  cows  can  be  discovered  which  are 
the  most  concerned  in  the  contamination  of  milk  with 
tubercle  bacilli.  Such  an  examination  should  include  a 
careful  inspection  and  palpation  of  the  udder  and  supra- 
mammary  lymph  glands ;  inspection  of  the  milk  in  each 
quarter;  palpation  of  the  other  superficial  lymph  glands; 
examination  of  the  general  condition  of  the  animal;  in- 
spection for  nasal  discharge;  examination  for  cough; 
examination  of  the  respiration;  auscultation  of  the  lungs ; 
examination  of  the  digestive  tract,  especially  for  chronic 


92  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

tympanites  and  diarrhoea,  and  inspection  for  vaginal 
discharge.  In  some  cases  it  will  also  be  necessary  to  take 
the  temperature  and  pulse  and  to  examine  the  lungs  and 
pleura  by  percussion  as  well  as  auscultation,  and  in  suspi- 
cious cases,  when  a  definite  decision  cannot  be  made,  it 
may  be  necessary  to  apply  the  tuberculin  test  to  the  ani- 
mal under  examination  or  to  collect  sputum  from  the 
trachea  or  oesophagus,  secretions  from  the  vagina,  scrap- 
ings from  the  rectum,  and  milk,  and  submit  them  to  a 
microscopic  examination  and  inoculation  test  (see  p. 
275).  In  tuberculin-testing  such  animals,  a  large  dose 
of  tuberculin  must  be  used,  from  two  and  one-half  to  five 
times  the  ordinary  dose.  When  the  microscopic  examina- 
tion of  material  from  an  animal  of  this  kind  gives  a  nega- 
tive result  it  cannot  be  accepted  as  final,  but  guinea  pigs 
must  be  inoculated.  If  death  does  not  occur  earlier,  the 
guinea  pigs  must  be  held  for  two  months  after  inoculation 
before  they  can  be  killed  for  post-mortem  examination. 
Most  owners  would  prefer  to  dispose  of  an  ordinary  cow 
on  suspicion  rather  than  feed  it  for  this  length  of  time 
and  keep  it  isolated  and  not  be  permitted  to  use  the  milk 
without  heating  it.  It  is  usually  more  satisfactory  to 
apply  the  tuberculin  test  in  such  cases.  Clinical  cases 
of  tuberculosis  are  usually  unthrifty  and  are  generally 
not  good  milkers  and  the  owner  can  usually  be  convinced 
that  such  animals  are  unprofitable.  Another  reason  for 
disposing  of  such  cows,  which  will  appeal  to  the  owner, 
is  that  they  are  sources  of  infection  for  the  other  cattle 
in  the  herd.  As  a  rule,  the  removal  of  animals  of  this 
kind,  advice  and  assistance  in  securing  healthy  cows  to 
replace  them,  and  proper  attention  to  the  other  features 
of  dairy  inspection  will  gain  the  confidence  of  the  owner 
rather  than  his  opposition,  and  after  a  system  of  inspec- 


INFLUENCE  OF  DISEASE  UPON  MILK  93 

tion  of  this  character  has  been  in  operation  for  several 
years  the  tuberculin  test  may  be  added  with  very  little 
objection.  Fewer  reactions  will  then  be  obtained  and 
the  reacting  animals  can  be  more  readily  replaced  with 
non-tuberculous  animals. 

When  milk  is  produced  especially  for  children's  use, 
however,  the  greater  susceptibility  of  children  to  tubercle 
bacilli  of  bovine  origin  must  be  taken  into  account,  and 
the  most  thorough  methods  for  protecting  milk  from  con- 
tamination with  tubercle  bacilli  should  be  applied. 
Children's  milk  should  therefore  be  obtained  only  from 
herds  which  are  tuberculin-tested  at  least  once  a  year  and 
which  are  subjected  to  a  physical  examination  at  least 
once  each  month. 

The  efficiency  of  the  clinical  examination  of  dairy 
cows  in  preventing  the  contamination  of  a  milk  supply 
with  tubercle  bacilli  as  compared  with  the  bacteriological 
examination  of  the  milk  for  the  presence  of  the  bacilli 
is  fairly  presented  in  the  following  statement  from  the 
report  of  the  British  Commission  on  tuberculosis :  "  The 
presence  of  tubercle  bacilli  in  cow's  milk  can  be  dis- 
covered, though  with  some  difficulty,  if  proper  means  be 
adopted,"  but  "  it  is  much  easier  to  demonstrate  with 
certainty  by  clinical  examination  that  a  cow  is  affected 
with  tuberculosis  and  will  in  consequence  perhaps  pro- 
duce tuberculous  milk."  Furthermore,  milk  from  a  cow 
eliminating  tubercle  bacilli  is  not  constantly  infected. 
On  certain  days,  the  organisms  may  be  absent  entirely 
or  present  in  only  small  numbers.  A  single  examination 
may  therefore  give  misleading  results. 

The  destruction  of  tubercle  bacilli  in  milk  by  heat 
is  considered  in  the  chapter  on  pasteurization  (page  203) . 


94          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Diagnosis  of  Tuberculosis  of  the  Udder. — For  a  time  after 
the  disease  has  been  established  in  the  udder,  the  tubercles  are 
not  large  enough  to  be  discovered  by  palpation  and  the  milk 
retains  its  normal  appearance,  but  during  this  initial  stage 
of  the  disease  symptoms  are  usually  present  in  other  organs 
which  enable  one  to  discover  the  presence  of  the  disease  by 
physical  examination.  In  119  cows  affected  with  tuberculosis 
of  the  udder,  Lungwitz  21  found  tuberculosis  in  other  organs 
in  every  one.  The  observations  of  Rick  and  of  Joest  and 
Kracht,  already  quoted,  show  that  the  disease  is  usually  gener- 
alized when  the  udder  becomes  infected. 

Tuberculosis  of  the  udder  runs  a  slow,  insidious  course. 
The  perceptible  changes  in  the  udder  which  indicate  its  presence 
are  firm  nodules,  which  are  neither  hot  nor  painful,  or  a  rather 
diffuse  painless  induration  without  local  increase  of  tempera- 
ture, in  one  or  more  quarters.  Later,  abscesses  may  form  and 
rupture  (mixed  infection) ;  atrophy  may  also  occur.  The 
posterior  quarters  are  most  commonly  affected.  The  supra- 
mammary  lymph  glands  may  be  enlarged,  while  the  udder  is  of 
normal  appearance,  but  in  these  cases  the  udder  is  usually  also 
infected.  In  rare  cases,  the  disease  runs  an  acute  course,  the 
udder  showing  the  symptoms  of  acute  inflammation. 

In  contrast  with  what  occurs  in  other  forms  of  udder  disease, 
the  milk  remains  of  normal  appearance  for  eight  to  ten  weeks, 
although  it  may  be  highly  virulent.  Finally,  it  becomes  thin 
and  transparent  like  water,  assumes  a  yellowish  color  and  con^ 
tains  small  clots  or  flakes.  When  it  is  permitted  to  stand,  a 
pus-like  sediment  is  deposited  with  a  yellow,  transparent  fluid 
resembling  seruml  above  it.  The  acidity  is  reduced  one-half 
(Raudnitz),  or  the  reaction  is  even  sometimes  alkaline  (Oster- 
tag).  In  advanced!  cases,  the  secretion  of  milk  ceases  and'  only 
a  purulent  fluid  in  moderate  amount  can  be  obtained  from  the 
affected  quarter. 

Diagnosis  of  Open  Tuberculosis. — (a)  Pulmonary  Tubercu- 
losis.— The  most  characteristic  symptom  is  a  chronic  cough,  at 

21  Leblanc,  Diseases  of  Mammary  Gland  (Nunn's  transla- 
tion). 


INFLUENCE  OF  DISEASE  UPON  MILK  95 

first  vigorous,  later  weak.  The  respiration  is  often  unchanged, 
but  in  advanced  cases  it  is  usually  rapid  and  labored.  Sometimes 
there  is  a  purulent  nasal  discharge.  Percussion  does  not 
usually  give  much  information ;  on  auscultation  increased  vesicu- 
lar murmur,  rales,  and  indefinite  sounds  may  be  detected.  These 
symptoms  are  usually  accompanied  by  anaemia,  unthr  if  tines  s, 
emaciation,  dull  and  sunken  eyes,  variable  or  poor  appetite, 
diarrhoea,  repeated  bloating  after  meals,  or  distention  of  the  ju- 
gular vein.  In  advanced  cases  the  pulse  is  accelerated  and  soft. 

(6)  Intestinal  Tuberculosis. — The  symptoms  of  intestinal 
tuberculosis  are  not  characteristic.  Repeated  attacks  of  colic 
and  constipation  alternating  with  diarrhoea  are  the  most  sus- 
picious. The  intestinal  discharges  may  be  quite  fluid  and 
frequently  contain  mucus  and  pus,  sometimes  blood.  The  diges- 
tive disturbances  which  are  nearly  always  present  in  advanced 
tuberculosis  are  usually  due  to  the  involvement  of  the  intestines, 
but  on  the  other  hand,  they  may  be  entirely  absent  when  the 
intestines  are  tuberculous. 

(c)  Tuberculosis  of  the  Uterus. — A  turbid,  mucous  or  muco- 
purulent  discharge,  yellowish  or  rather  ichorous  and  of  foul 
odor,  is  a  constant  symptom  of  tuberculosis  of  the  uterus.  Frag- 
ments of  caseous  material  or  streaks  of  blood  are  sometimes 
present.  The  cow  is  sterile  and  frequently  in  heat.  On  rectal 
examination  the  sacral  lymph-glands  may  be  found  enlarged  or 
the  horns  of  the  uterus  hard  and  nodular. 

When  the  mucous  membrane  of  the  vagina  or  vulva  is  tuber- 
culous, ulcers  or  nodules  are  present,  together  with  a  similar 
discharge. 

Enlargement  of  the  superficial  lymph  glands  is  an  important 
symptom. 

While  these  symptoms  in  themselves  are  not  sufficient  to 
justify  a  positive  diagnosis  of  tuberculosis,  nevertheless  when 
they  are  presented  by  an  animal  in  a  herd  in  which  tuberculosis 
is  known  to  exist,  and  when  other  possible  causes  for  them  can 
be  excluded,  an  error  will  not  often  be  made  if  the  animal  is 
regarded  as  tuberculous.  In  doubtful  cases  the  tuberculin  test 
can  be  applied  or  a  microscopic  examination  or  an  inoculation 
test  made. 


96  PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

APHTHOUS  FEVER  OR  FOOT  AND  MOUTH  DISEASE 

In  the  milder  forms  of  foot  and  mouth  disease  the 
milk  secretion  may  not  be  affected,  but  in  the  more  severe 
cases  the  milk  flow  is  reduced  one-half  and  the  milk  is  con- 
siderably changed  in  composition  and  appearance.  The 
alterations  are  similar  to  those  observed  in  inflammation 
of  the  udder.  The  albumin,  globulin  and  salts  are  in- 
creased in  quantity,  while  the  sugar,  casein,  and  usually 
the  fat  are  decreased,  although  sometimes  the  fat  is  in- 
creased. The  milk  becomes  thin,  and  after  it  stands 
for  a  while  a  layer  of  slimy,  dirty  cream  forms  at  the 
top  of  the  fluid  and  considerable  sediment  is  deposited 
at  the  bottom  of  the  vessel.  When  examined  microscopic- 
ally, the  sediment  is  found  to  be  rich  in  cells — epithelial 
cells,  leucocytes,  and  red-blood  cells.  The  milk  coagu- 
lates when  boiled,  reacts  positively  to  the  alcohol  test  and 
contains  a  large  amount  of  catalase. 

Nocard  has  shown  that  the  milk  of  affected  cows  does 
not  contain  the  virus  of  foot  and  mouth  disease  when  it 
is  drawn  from  the  udder  in  a  manner  which  pre- 
vents external  contamination,.  But  when  vesicles  or 
ulcers  are  present  on  the  teats  or  udder  it  is  not  possible 
to  draw  milk  in  the  ordinary  way  without  it  becoming 
contaminated  with  the  virus.  Merely  a  trace  of  the  serum 
from  the  vesicles  is  sufficient  to  render  50  to  100  quarts 
of  milk  infectious.  Practical  experience  indicates  that 
the  milk  of  affected  cows  is  frequently  infectious.  Fur- 
thermore, the  extraordinary  facility  with  which  the  virus 
is  disseminated  makes  it  extremely  probable  that  all  of 
the  milk  of  a  herd  in  which  the  disease  exists  may  be 
infected  secondarily. 

The  disease  may  be  transmitted  to  man  through  milk, 


INFLUENCE  OF  DISEASE  UPON  MILK  97 

and  also  to  cattle  and  swine.  It  may  also  be  transmitted 
by  butter  and  cheese.  Man  may  be  mildly  or  severely 
affected;  in  some  instances,  the  disease  has  terminated 
fatally.  The  symptoms  are  fever,  weakness,  conjuncti- 
vitis, nausea,  vomiting,  and  diarrhoea,  with  formation  of 
vesicles  on  the  mucous  membrane  of  the  lips,  mouth  or 
nose,  and  on  the  ears,  fingers  or  other  places  on  the  body; 
sometimes  the  skin  is  red  and  the  joints  painful. 

The  sale  of  milk  from  herds  in  which  foot  and  mouth 
disease  exists  should  not  be  permitted,  unless  it  is  heated 
sufficiently  to  destroy  the  virus  and  is  not  changed  in 
appearance.  The  virus  is  not  very  resistant.  A  tempera- 
ture of  50°  C.  (122°  F.)  for  15  minutes;  70°  C.  (168°  F.) 
for  10  minutes;  or  85°  C.  (185°  F.)  momentarily  will 
destroy  it  (Ernst). 

COWPOX 

Cowpox  is  closely  related  to  variola  or  smallpox  of 
man.  Before  vaccination  was  introduced,  when  smallpox 
frequently  became  epidemic,  it  is  very  probable  that  cow- 
pox  often  originated  from  this  source.  Vaccinia  of  man  is 
also  transmissible  to  cattle  and  many  instances  are  on 
record  in  which  cows  have  been  infected  by  vaccinated 
persons.  Infection  takes  place  during  milking  as  a  rule, 
the  contagion  being  rubbed  into  the  skin  of  the  teat  by 
the  hands  of  the  milker.  The  disease  is  therefore  most 
commonly  seen  in  cows  in  milk.  It  usually  begins  with  a 
rise  of  temperature,  but  this  may  pass  unnoticed  unless 
it  is  accompanied  by  dullness  and  loss  of  appetite,  as  is 
sometimes  the  case.  The  teats  and  neighboring  parts  of 
the  udder  become  swollen,  hot,  and  painful.  In  two  or 
three  days,  papules  appear,  which  may  be  as  large  as  a 
pea  and  which  are  surrounded  by  a  red  area.  On  the 

7 


98          PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

udder  they  are  round;  on  the  teats  oblong,  with  the  great- 
est diameter  parallel  with  the  length  of  the  teat.  In  a 
day  or  two  they  change  into  vesicles  of  a  bluish-white 
or  yellowish- white  color.  The  vesicles  ripen  into  pustules 
in  eight  or  ten  days  and  a  depression  or  umbilication 
appears  in  the  top,  after  which  they  rupture  and  leave 
an  ulcer,  or  dry  and  heal  under  a  scab.  They  may  be 
ruptured  during  milking  before  they  are  ripe. 

The  milk  may  become  thin,  bluish,  and  of  lighter 
specific  gravity  than  normal;  it  may  be  nauseating  and 
may  coagulate  very  readily.  The  acidity  may  be  below 
normal.  These  changes,  however,  do  not  always  occur. 
When  the  disease  is  complicated  with  parenchymatous 
mastitis,  as  sometimes  happens,  then  the  milk  undergoes 
the  pronounced  changes  which  occur  in  the  latter  con- 
dition (see  page  109). 

Cowpox  is  transmitted  from  cow  to  cow  by  the  milker 
and  by  infected  bedding,  fodder,  and  stalls.  The  disease 
is  also  transmissible  from  the  cow  to  man  through  milk. 
There  is  no  proof  that  the  virus  is  excreted  through  the 
udder,  but  as  the  pox  are  located  on  the  teats  and  the 
adjacent  parts  of  the  udder  it  is  practically  impossible 
to  draw  the  milk  without  the  virus  contained  in  the  ves- 
icles and  pustules  getting  into  it.  Stern  saw  cowpox 
transmitted  to  a  large  number  of  children  by  milk  from 
a  dairy  in  which  the  disease  was  enzootic.  The  children 
were  affected  with  an  eruption  on  the  face  which  healed 
under  a  scab.  Not  many  such  observations  have  been 
recorded,  however.  The  reason  for  this  is  that  the  general 
custom  of  vaccinating  against  smallpox  has  rendered 
most  persons  immune  to  the  disease.  The  transmission 
of  the  disease  to  the  milkers  by  direct  infection  of  wounds 
on  the  hands  or  fingers  has  been  more  frequently  ob- 


INFLUENCE  OF  DISEASE  UPON  MILK  99 

served;  in  some  cases  the  face  has  been  affected  in  this 
way. 

Milk  from  cows  affected  with  cowpox  should  not  be 
used  for  food.  When  the  disease  is  enzootic,  the  healthy 
and  diseased  cows  should  be  separated  and  separate 
milkers  provided  for  each  class.  This  is  especially  im- 
portant when  the  milk  is  to  be  used  by  children.  The 
virus  of  cowpox  is  destroyed  by  a  temperature  of  48°  C. 
(119°  F.).  Milk  from  infected  animals  which  has  not 
undergone  any  physical  change  and  milk  which  has  been 
exposed  to  infection  may  be  rendered  safe  by  heating  to 
this  temperature. 

False  Cowpoac. — Cowpox  should  not  be  confused  with 
a  condition  more  commonly  affecting  the  udder  which 
is  known  as  false  cowpox.  In  this  condition,  small  nodu- 
lar swellings  which  may  be  as  large  as  a  pea  appear  on 
the  teats  and  neighboring  parts  of  the  udder,  rupture  in 
a  few  days,  and  then  heal  under  a  scab.  The  teats  are 
not  hot,  swollen  or  tender  and  there  is  no  red  area  around 
the  nodules,  as  in  true  cowpox ;  fever  is  also  absent.  The 
condition  is  supposed  to  be  caused  by  the  ordinary  pyo- 
genic  cocci,  which  are  rubbed  into  the  skin  during  milk- 
ing or  enter  through  wounds.  Cows  with  teats  covered 
with  a  fine  skin  seem  to  be  most  susceptible.  The  condition 
may  be  transmitted  from  cow  to  cow  by  the  hands  of 
the  milker,  but  is  not  transmissible  to  man.  The  milk  is 
not  affected  except  in  so  far  as  it  may  be  contaminated 
with  purulent  matter  from  the  ruptured  nodules.  There 
is  only  a  small  quantity  of  this  material  and  the  con- 
tamination from  this  source  therefore  can  only  be  very 
slight. 

Furunculosis  of  the  Udder  is  sometimes  called  cowpox 
by  dairymen.  This  condition  usually  occurs  sporadically, 


100        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

but  it  is  occasionally  enzootic,  especially  when  musty 
or  mouldy  straw  is  used  for  bedding.  It  is  most  fre- 
quently seen  in  fresh  cows,  after  they  have  been  put  on 
full  feed,  and  it  is  probably  for  this  reason  that  the  fu- 
runcles are  spoken  of  as  feed  boils.  Firm,  painful,  nodu- 
lar swellings,  varying  in  size  from  a  pea  to  a  walnut, 
appear  in  the  subcutaneous  tissue  of  the  udder.  In 
seven  or  eight  days  a  dark  area  of  puriform  softening 
develops  in  the  centre  of  each  individual  swelling,  which 
subsequently  ruptures  at  this  point  and  discharges  its 
contents  of  pus  mixed  with  shreds  of  tissue.  This  dark 
patch,  or  the  scab  of  dried  blood  which  subsequently 
forms  at  the  point  of  rupture,  has  given  the  process  the 
popular  name  of  black  scab  in  some  sections.  The  milk 
secretion  is  not  affected,  but  the  milk  may  be  contami- 
nated secondarily  with  the  purulent  discharge. 

ANTHRAX 

The  question  of  using  the  milk  from  a  cow  affected 
with  anthrax  does  not  often  arise  in  practice  because, 
as  a  rule,  the  milk  secretion  ceases  suddenly  with  the  onset 
of  the  fever,  while  in  those  cases  in  which  it  continues 
it  is  reduced  to  a  small  quantity  and  is  very  much  changed 
in  appearance.  It  is  more  yellowish  than  normal,  slimy, 
sometimes  bloody,  with  a  bitter  taste,  and  after  standing 
undisturbed  for  a  few  hours  separates  into  a  layer  of  cream 
and  of  serum.  Anthrax  bacilli  are  excreted  through  the 
udder  only  in  the  advanced  stages  of  the  disease,  after  they 
have  invaded  the  blood  stream  and  when  the  udder  is 
affected.  But  the  chances  of  milk  becoming  infected 
secondarily  are  very  great.  The  bloody  discharges  and 
the  manure  from  infected  animals  contain  the  anthrax 


INFLUENCE  OF  DISEASE 'tlEON  MIL&  '•*/•          101 

bacilli  and  their  spores,  and  the  spores  may  also  be 
present  in  the  dust  of  the  stable  and  in  the  dust  of  straw 
and  hay  from  infected  fields.  The  organisms  may  gain 
access  not  only  to  the  milk  of  the  affected  cow,  but  also 
to  the  milk  of  other  cows  in  the  stable.  Anthrax  bacilli 
and  spores  entering  milk  in  this  way  may  multiply 
rapidly,  as  milk  is  an  excellent  culture  medium  for  this 
organism.  While  the  bacilli  are  digested  by  the  gastric 
juice,  the  spores  are  not  affected  and  in  disturbances  of 
digestion  the  bacilli  may  also  escape  destruction.  .  Ernst 
mentions  a  typhoid  fever  patient  who  developed  intestinal 
anthrax  after  drinking  milk  from  a  cow  with  a  malignant 
pustule  on  the  udder. 

All  milk  from  a  herd  in  which  anthrax  is  present 
must  therefore  be  regarded  as  dangerous  to  man  until 
proper  precautions  are  taken  to  prevent  the  secondary 
infection  of  the  milk  from  the  cows  which  are  not  diseased. 
Diseased  and  dead  animals  should  be  at  once  removed 
from  the  stable,  which  should  be  thoroughly  cleaned  and 
disinfected.  McFadyean  recommends  that  the  tempera- 
ture of  every  exposed  cow  be  taken  each  day  before  milk- 
ing for  seven  to  ten  days,  and  that  all  those  showing  a  rise 
of  temperature  be  treated  as  suspicious  cases  and  taken 
out  of  the  stable,  the  milk  not  being  used. 

RABIES 

Cattle  are  usually  infected  with  rabies  by  being 
bitten  by  a  rabid  dog.  Frequently  several  animals  in  a 
herd  are  infected  at  the  same  time.  While  the  virus  of 
rabies  is  to  be  found  in  its  purest  and  most  concentrated 
form  in  the  central  nervous  system,  it  is  also  present  in 
the  milk  of  affected  animals  as  well  as  in  the  secretions 


102         PRINCIILES  AND  PRACTICE  OF  MILK  HYGIENE 

of  the  salivary  and  lachrymal  glands  and  pancreas. 
Numerous  feeding  experiments  with  milk  and  other  sub- 
stances from  rabid  animals  show  that  the  virus  is  not 
absorbed,  and  that  the  disease  is  not  produced,  when  the 
mucous  membrane  of  the  digestive  tract  is  intact  and  the 
digestive  functions  are  acting  normally.  In  the  upper 
part  of  the  digestive  tract,  stratified  squamous  epithelium 
acts  as  a  barrier  to  the  entrance  of  the  virus  into  the  blood 
stream  and  when  it  reaches  the  stomach  it  is  digested  by 
the  gastric  juice.  But  when  wounds  are  present  in  the 
mucous  membrane  of  the  lips,  mouth  or  throat,  or  when 
the  secretion  of  gastric  juice  is  disturbed,  the  ingestion 
of  milk  containing  the  virus  of  rabies  may  produce  the 
disease.  Milk  from  cows  affected  with  rabies  must  there- 
fore be  regarded  as  dangerous.  Whether  the  milk  of 
infected  cows  contains  the  virus  before  symptoms  of  the 
disease  appear,  as  is  the  case  with  the  saliva  of  dogs,  is 
not  known.  Until  this  question  is  determined  it  will  be 
advisable  not  to  use  the  milk  of  a  cow  which  has  been 
bitten  by  a  rabid  dog  until  it  is  determined  that  infection 
did  not  occur. 

ACTINOMYCOSIS 

Actinomycosis  usually  affects  the  maxillae,  tongue  or 
other  parts  about  the  head,  but  it  sometimes  occurs  in 
the  udder,  also  in  the  lungs  and  other  internal  organs. 
When  present  in  the  udder  it  is  usually  of  primary 
origin,  i.e.,,  the  infection  enters  through  the  teat  canal. 
Actinomycosis  of  the  udder  is  generally  indicated  by  the 
presence  of  one  or  several  firm  nodules  of  the  size  of  a 
bean  up  to  a  hen's  egg  in  one  or  more  quarters  of  the 
organ.  These  nodules  consist  of  a  thick  wall  of  connec- 
tive tissue  surrounding  a  purulent  centre  in  which  the 
actinomyces  may  be  seen  in  the  form  of  sulphur-yellow 


INFLUENCE  OF  DISEASE  UPON  MILK  103 

granules.  They  may  rupture  internally  or  externally 
and  discharge  pus  containing  the  fungi.  The  milk  cis- 
tern may  be  filled  with  the  nodules.  Sometimes  the  dis- 
ease appears  in  the  udder  in  a  miliary  form;  the  affected 
quarters  are  enlarged,  hard  and  somewhat  nodular,  and 
on  section  numerous  very  small  nodules  of  granulation 
tissue  with  softened  purulent  centres  are  found  dissemi- 
nated through  the  gland  tissue.  Similar  nodules  may  be 
found  on  the  mucous  membrane  of  the  larger  canals  and 
cistern.  Numerous  actinomyces  are  found  in  the  soft- 
ened centre  of  the  nodules.  As  a  rule,  actinomycosis 
of  the  udder  has  not  been  recognized  until  after  the 
slaughter  of  the  affected  animal,  consequently  nothing 
definite  is  known  regarding  the  appearance  of  the  milk 
in  this  condition.  Up  to  this  time,  actinomyces  have  not 
been  demonstrated  in  milk,  but  they  are  no  doubt  ex- 
creted with  the  milk  when  the  actinomycotic  nodules  rup- 
ture into  an  alveolus  or  duct  of  the  udder.  The  milk 
may  be  infected  secondarily  when  an  actinomycotic 
nodule  in  the  udder  ruptures  externally  or  when  an  actin- 
omycotic tumor  in  the  maxilla  or  adjacent  parts  opens. 
In  such  cases  the  discharge  contains  not  only  actinomyces 
but  also  bacteria,  particularly  the  pyogenic  organisms, 
and  these,  too,  may  gain  access  to  the  milk. 

There  is  no  record  of  the  transmission  of  actinomy- 
cosis to  man  through  milk.  This  may  be  due  in  part  to 
the  slow  development  of  the  disease,  as  in  the  case  of 
tuberculosis.  Infection  with  actinomyces  may  occur  in 
man,  as  it  does  in  cattle,  through  the  food,  especially 
when  wounds  exist  in  the  mouth  or  other  anterior  parts 
of  the  digestive  tract.  Since  there  is  a  possibility  of  the 
transmission  of  this  disease  by  milk,  it  is  advisable  to 
exclude  from  dairies  all  cows  with  actinomycosis  of  the 


104        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

udder  or  with  open,  discharging  actinomycotic  tumors. 
Milk  from  cows  in  the  latter  condition  is  further  objec- 
tionable because  it  may  contain  pus  and  pyogenic  or- 
ganisms, and,  in  advanced  cases,  for  the  additional  reason 
that  the  general  condition  is  affected,  the  animal  becom- 
ing emaciated,  weak  and  dull. 

MILK  SICKNESS  OR  TREMBLES 

Cattle  and  horses  when  pastured  on  certain  lands  in 
circumscribed  areas  in  the  United  States  develop  a  dis- 
ease known  as  milk  sickness  or  trembles.  Its  etiology 
has  been  the  subject  of  much  speculation  and  investiga- 
tion. In  1907  Jordan  and  Harris  isolated  in  pure  culture 
from  the  blood  and  organs  of  animals  dead  of  the  disease 
a  spore-forming  bacillus  with  which  they  succeeded  in 
reproducing  the  disease  in  experimental  animals.  They 
have  given  this  organism  the  name  of  Bacillus  lactimorbL 
The  principal  symptoms  of  the  disease  are  violent  trem- 
bling and  great  restlessness,  followed  by  paralysis.  The 
animal  may  fall  and  die  suddenly,  but  usually  it  lies  sev- 
eral days  in  a  paralyzed  condition.  The  disease  is  trans- 
mitted to  man  through  the  milk,  butter,  and  meat  from 
affected  animals.  The  symptoms  in  man  are  severe 
vomiting,  difficult  breathing,  subnormal  temperature, 
paralysis,  and  death. 

II.  DISEASES  OF  CATTLE  WHICH  MAY  RENDER  MILK 
HARMFUL  TO  MAN. 

INFLAMMATION  OF  THE  UDDER— MASTITIS 

Cows  are  very  frequently  affected  with  mastitis,  a 
disease  of  great  economic  as  well  as  hygienic  importance. 
There  are  three  forms  of  the  disease :  ( 1 )  Catarrhal  mas- 
titis, which  may  be  either  mucous  or  purulent,  and  which 


INFLUENCE  OF  DISEASE  UPON  MILK  105 

runs  a  subacute  or  chronic  course;  (2)  parenchymatous 
mastitis,  which  is  purulent  and  acute,  and  which  is  some- 
times accompanied  by  abscess  formation  and  gangrene, 
and  (3)  interstitial  mastitis,  which  may  be  a  simple  in- 
flammation or  a  phlegmonous  condition.  The  three  forms 
differ  in  the  type  of  the  inflammation  (acute  or  chronic) , 
the  part  of  the  udder  tissue  affected,  the  effect  upon  the 
milk  secretion,  and  in  the  character  of  the  bacteria  con- 
cerned. One  form  may  be  associated  with  another.  The 
disease  is  commonly  called  "  garget "  by  dairymen  and 
farmers. 

1.  Catarrhal  Mastitis. — From  a  hygienic  standpoint, 
catarrhal  mastitis  is  of  greatest  importance  because  it 
occurs  more  frequently  than  the  other  forms  and  also 
because  the  milk  may  contain  the  causative  bacteria  be- 
fore clinical  symptoms  or  marked  changes  in  the  milk 
are  apparent  and  for  a  time  after  they  have  disappeared. 
This  latter  circumstance  has  been  the  inspiration  of 
numerous  efforts  to  discover  a  method  of  examining  milk 
by  which  this  disease  could  be  detected  in  its  incipiency. 

Catarrhal  mastitis  is  a  mucous  or  purulent  catarrh 
of  the  mucous  membrane  of  the  teat  canal,  milk  cistern, 
and  large  milk  ducts.  It  is  frequently  accompanied  or 
followed  by  a  productive  inflammation  of  the  submucous 
and  interstitial  connective  tissue,  in  which  case  it  often 
terminates  in  atrophy  of  the  gland  tissue  and  loss  of 
function.  It  is  usually  caused  by  streptococci  of  varying 
degrees  of  virulence;  sometimes,  but  not  often,  mucous 
catarrh  occurs  without  the  intervention  of  bacteria  from 
the  effects  of  cold  or  overfeeding.  The  symptoms  are 
never  pronounced.  The  history  of  the  cow  is  of  great 
assistance  in  detecting  incipient  cases,  although  it  is 
sometimes  difficult  to  obtain.  A  statement  that  the  cow 


106        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

"  milks  hard,"  i.e.>  that  there  is  difficulty  in  expressing 
the  milk  through  the  teat  canal,  or  that  the  milk  is  not 
"let  down  "  or  is  "  drawn  up,"  or  that  the  cow  has  recently 
developed  a  tendency  to  kick  during  milking,  should  ex- 
cite suspicion  of  the  presence  of  the  disease.  The  first 
condition  is  due  to  obstruction  of  the  teat  canal  by  swell- 
ing of  the  mucous  membrane  or  by  dried  secretion;  the 
others  occur  because  milking  is  painful.  Among  the 
first  noticeable  symptoms  of  the  disease  are  changes  in 
the  milk  stream  expressed  from  the  teat.  This  may  be 
split,  deflected  from  the  proper  direction,  or  it  may  not 
be  cut  off  promptly  and  may  therefore  smear  the  end  of 
the  teat — all  indications  of  catarrh  of  the  mucous  mem- 
brane of  the  teat  canal.  In  such  cases  small  yellow  crusts 
may  be  found  covering  the  opening  of  the  teat  canal,  but 
crusts  of  dried  milk  may  also  be  present  at  this  point  when 
the  sphincter  of  the  teat  canal  does  not  close  properly. 
When  pressure  is  exerted  upon  the  lower  end  of  the  teat, 
a  drop  of  pus  or  mucus  may  be  squeezed  out  of  the  teat 
canal  or  the  thickened  mucous  membrane  may  project 
through  the  opening.  Later,  the  mucous  membrane  of 
the  cistern  may  become  thickened,  in  which  case  a  cord 
about  as  thick  as  a  lead  pencil  is  felt  running  through  the 
middle  of  the  teat  when  the  teat  is  rolled  between  the 
thumb  and  fingers.  Flat,  disc-shaped  thickenings  about 
the  size  of  a  quarter  dollar  and  nodular  indurations  may 
be  present  in  the  upper  limits  of  the  cistern  when  the 
mucous  membrane  of  the  lower  end  of  the  large  milk 
ducts  is  thickened.  Growths  upon  the  wall  of  the  cistern 
or  teat  canal  ("  spider  in  the  teat ")  may  also  be  dis- 
covered by  palpation.  The  induration  usually  extends 
slowly  into  the  interstitial  tissue,  generally  from  the  teat 


INFLUENCE  OF  DISEASE  UPON  MILK  107 

upward,  producing  a  hard  firm  area  ("cake,"  "caked 
udder,"  "  cold  garget  "),  which  may  eventually  involve 
the  entire  quarter.  The  newly  formed  connective  tissue 
subsequently  contracts  and  causes  atrophy  of  the  gland 
tissue  and  loss  of  function. 

In  the  early  stages  of  the  disease,  and  also  throughout 
mild  cases  of  mucous  catarrh,  the  milk  does  not  show  any 
marked  change  at  the  time  it  is  drawn  from  the  udder. 
Very  often  it  contains  small  flakes,  some  of  which  may 
be  as  small  as  a  pin-head;  they  may  be  present  only  in 
the  first  milk  drawn,  but  sometimes  they  do  not  appear 
until  the  middle  or  at  the  end  of  the  milking.  After  the 
milk  stands  for  a  time,  or  is  centrifugalized,  a  grayish- 
yellow  sediment  is  deposited  and  a  dirty-gray,  clumpy 
or  granular  cream  layer  is  formed.  In  severe  cases  of 
mucous  catarrh,  the  secretion  becomes  slimy  and  viscid. 
In  purulent  catarrh,  the  secretion  of  milk  decreases 
while  the  pus  cells  and  fibrin  increase  and  the  fluid  ob- 
tained from  the  affected  quarter  gradually  changes  to 
a  thick,  yellowish,  purulent  exudate  or  to  a  yellowish 
serum  containing  clumps  of  pus  and  fibrin.  Frequently, 
the  exudation  ceases  entirely  and  the  milk  secretion  does 
not  return  until  the  next  lactation  or  not  at  all.  The 
chemical  composition  of  the  milk  is  only  slightly  changed 
at  the  beginning  of  the  disease,  the  lactose  being  de- 
creased and  the  mineral  salts,  especially  the  sodium  chlo- 
ride, increased,  while  the  other  constituents  are  present 
in  the  usual  amount.  Later,  there  is  a  greater  decrease 
in  the  lactose,  the  casein  is  also  below  normal,  and  the 
fat  is  usually  decreased,  while  the  albumin,  globulin,  and 
mineral  salts  are  increased.  Fibrin  is  also  present.  The 
reaction  of  the  milk  is  usually,  but  not  always,  alkaline. 
The  taste  is  salty  or  bitter.  Cells  are  present  in  large 


108        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

numbers  in  the  sediment  and  cream,  especially  the  poly- 
morphonuclear  leucocytes  in  purulent  catarrh.  The 
catalase  content  is  increased.  Coagulation  occurs  when 
the  alcohol  or  the  boiling  test  (see  pages  284,  285)  is 
applied. 

On  account  of  the  difficulty  of  detecting  catarrhal 
mastitis  in  its  early  stages,  the  determination  of  the  leuco- 
cytic  content  of  samples  of  market  milk  has  sometimes 
been  relied  on  to  discover  the  presence  of  the  disease.  It 
has  been  demonstrated  that  cases  of  catarrhal  mastitis 
may  be  detected  by  this  method  but  we  have  no  means  of 
knowing  how  many  of  such  cases  escape  discovery;  there 
is  reason  to  believe  that  many  are  overlooked.  The  ex- 
amination of  samples  of  milk  from  individual  cows  by 
means  of  the  catalase  test  is  the  most  efficient  method  of 
detecting  the  disease  (see  page  287).  When  numerous 
very  small,  punctiform,  brownish  colonies  appear  in  the 
plates  prepared  for  determining  the  number  of  bacteria  in 
milk  and  these  are  found  upon  microscopic  examination  to 
consist  of  streptococci  in  long  chains,  an  examination  of 
the  herd  will  usually  discover  the  presence  of  one  or  more 
cases  of  catarrhal  mastitis. 

A  special  form  of  purulent  catarrhal  mastitis  which 
leads  to  multiple  abscess  formation  is  caused  by  the  Bacil- 
lus pyogenes.  The  secretion  has  a  foul  odor.  The  disease 
occurs  most  commonly  in  "  dry  "  cows,  but  is  usually  not 
discovered  until  they  become  "  fresh." 

2.  Parenchymatous  Mastitis. — The  detection  of  this 
form  of  mastitis  offers  no  difficulties  to  the  dairy  inspec- 
tor. It  is  attended  with  an  immediate  and  pronounced 
swelling  of  the  affected  portion  of  the  udder  and  the  milk 
at  once  presents  marked  changes.  As  the  name  indicates, 
it  is  an  inflammation  of  the  alveoli  and  small  tubules  of 


INFLUENCE  OF  DISEASE  UPON  MILK  109 

the  udder  and  is  usually  caused  by  the  Bacillus  phleg- 
masia  uberis  or  other  varieties  of  colon  bacilli,  sometimes 
by  organisms  of  the  paracolon  or  paratyphus  group,  the 
enteriditis  bacillus  or  by  staphylococci.  Septicaemia  may 
develop  in  the  course  of  the  disease.  Severe  cases  may 
terminate  in  gangrenous  mastitis.  In  the  beginning  of 
the  disease,  and  throughout  mild  cases,  a  turbid  fluid 
resembling  whey  in  appearance  and  containing  flakes  of 
casein,  is  obtained  from  the  affected  quarter.  Later,  in 
cases  of  medium  degree,  the  fluid  resembles  serum  and 
contains  clots  of  fibrin.  In  the  more  severe  cases,  the 
secretion  is  discolored  with  blood.  In  gangrenous  mas- 
titis, a  small  amount  of  bloody-serous,  dark,  foul-smelling 
fluid,  which  contains  gas  bubbles,  may  be  obtained  from 
the  affected  quarter.  The  chemical  changes  which  occur 
in  the  milk  in  parenchymatous  mastitis  are  similar  to  those 
which  take  place  in  catarrhal  mastitis.  There  is  a  de- 
crease in  the  lactose,  which  is  sometimes  entirely  absent ; 
the  fat  is  usually  decreased,  although  sometimes  it  is  in- 
creased; the  casein  is  decreased,  while  the  albumin,  glob- 
ulin, and  salts,  especially  sodium  chloride,  are  increased. 
The  taste  is  salty  or  bitter.  There  is  an  increase  in  the 
content  of  catalase  and  coagulation  takes  place  when  the 
alcohol  or  boiling  test  is  applied. 

3.  Interstitial  Mastitis. — The  simple,  traumatic  form 
of  interstitial  mastitis,  in  which  the  inflammatory  process 
is  limited  in  extent  and  rather  mild,  has  no  important 
effect  upon  the  milk  secretion,  but  when  the  disease  is 
due  to  the  entrance  of  bacteria  through  fissures  or 
wounds,  as  is  most  frequently  the  case,  a  phlegmonous 
inflammation  occurs  in  the  subcutaneous  or  interstitial 
connective  tissue  which  is  accompanied  by  a  rise  of  the 
body  temperature,  sometimes  to  107°  F.,  and  other  symp- 


110         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

toms  of  constitutional  disturbance.  There  is  then  more 
or  less  extensive  and  painful  swelling  of  the  affected 
quarter  which  begins  at  the  teats  and  extends  upward. 
The  milk  secretion  is  somewhat  reduced  in  quantity  in 
the  beginning  of  the  disease,  but  is  otherwise  unchanged. 
Later,  the  secretion  from  the  affected  quarter  is  dimin- 
ished ;  the  fat  is  decreased  and  the  milk  has  a  pale,  watery 
appearance.  The  inflammation  may  extend  into  the 
gland  tissue,  in  which  case  the  milk  will  undergo  the  same 
changes  as  in  parenchymatous  mastitis. 

Harmful  Properties  of  Mastitis  Milk. — In  mastitis 
the  secretion  from  the  udder  nearly  always  contains  bac- 
teria which  may  be  harmful  to  man.  In  the  catarrhal 
form  streptococci  are  usually  present,  sometimes  staphy- 
lococci  or  the  Bacillus  pyogenes.  In  the  parenchymatous 
form  bacteria  of  the  colon  group  are  usually  present, 
sometimes  bacilli  of  the  paratyphus  or  paracolon  group, 
the  enteriditis  bacillus,  or  staphylococci.  In  catarrhal 
mastitis  the  bacteria  may  be  present  when  the  milk  is  of 
normal  appearance  and  before  clinical  symptoms  appear 
and  also  after  the  clinical  symptoms  have  subsided  and 
the  milk  has  again  become  normal  in  appearance.  Bac- 
teria not  only  occur  in  the  secretion  from  the  affected 
quarter  but  they  may  also  be  present  in  the  milk  from  the 
other  quarters.  The  skin  of  the  teats  and  udder  is  con- 
taminated by  the  secretion  from  the  diseased  quarter  and 
some  of  this  infected  material  can  easily  fall  into  the  milk 
pail  during  the  drawing  of  milk  from  the  other  quarters. 
Secondary  infection  of  the  milk  is  also  likely  to  occur 
when  the  secretion  from  the  diseased  quarter  is  milked 
onto  the  floor,  as  is  frequently  done.  The  mastitis  bac- 
teria find  an  excellent  culture  media  in  milk  and  rapidly 
multiply  when  the  milk  is  kept  at  room  temperature. 


INFLUENCE  OF  DISEASE  UPON  MILK  111 

Considering  the  frequency  of  the  catarrhal  and  paren- 
chymatous  forms  of  mastitis  in  dairy  cows,  cases  of 
illness  in  man  resulting  from  the  ingestion  of  milk  from 
cows  affected  with  this  disease  have  not  been  reported  as 
often  as  would  be  expected.  There  are  several  reasons 
for  this.  The  milk  from  a  diseased  cow  may  be  diluted 
with  milk  from  cows  in  normal  condition  to  such  an  extent 
as  to  render  the  mixed  milk  harmless.  Furthermore, 
some  of  the  mastitis  bacteria  have  a  relatively  low 
virulence  for  man.  Finally,  it  rarely  happens  that  the 
physician  is  able  to  establish  the  connection  between  the 
disease  in  his  patient  and  the  cow  affected  with  mastitis, 
even  when  milk  from  the  latter  is  the  cause  of  the  disease. 
Nevertheless,  there  are  on  record  numerous  cases  of  ill- 
ness in  man  caused  by  the  ingestion  of  milk  from  cows 
affected  with  mastitis,  the  symptoms  in  these  cases  being 
nausea,  vomiting,  and  diarrhoea,  sometimes  associated 
with  fever,  f  aintness,  languor,  and  cramps  in  the  legs.  In 
two  instances  the  milk  which  was  the  cause  of  the  disease 
had  been  boiled.  It  is  not  known  whether  the  illness  in 
these  cases  was  due  to  a  heat-resisting  toxin  or  to  bacteria 
which  survived  the  heat  because  of  the  protection  fur- 
nished by  the  membrane  which  forms  on  the  surface  of 
milk  when  it  is  heated. 

Numerous  epidemics  of  septic  sore  throat  have  been 
reported  in  which  the  infection  was  transmitted  by  milk. 
In  some  of  these  epidemics,  cows  affected  with  strepto- 
coccic  mastitis  were  found  to  be  the  source  of  the  infec- 
tion, but  in  the  other  outbreaks  the  circumstances  seemed 
to  point  to  the  infection  of  the  milk  by  dairy  workers  suf- 
fering from  the  disease.  To  account  for  the  persistence  of 
streptococci  for  several  days  in  the  milk  supplies  involved 
in  the  second  group  of  epidemics,  the  theory  has  been 


112        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

advanced  by  Theobald  Smith  that  the  offending  organ- 
isms were  introduced  into  the  udder  of  some  of  the  cows 
by  infected  milkers,  multiplied  there  without  producing 
any  changes  in  the  organ  or  in  the  milk,  and  were  elimi- 
nated in  the  milk  in  large  numbers  at  each  milking.  In 
two  of  the  epidemics  in  the  United  States  (Chicago 
1911,  Baltimore  1912) ,  the  milk  which  spread  the  disease 
had  been  subjected  to  a  pasteurizing  process.  Rosenau 
observed  that  when  the  Streptococcus  pyogenes  is  grown 
in  raw  milk  it  is  modified  to  correspond  with  the  strepto- 
coccus of  epidemic  sore  throat. 

Milk  from  cows  affected  with  catarrhal  and  paren- 
chymatous  mastitis  is  also  objectionable  because  the  pus 
which  it  contains  often  gives  it  an  unpleasant  taste  and 
frequently  causes  it  to  putrefy  and  to  curdle  quickly. 
The  pus  itself  may  be  harmful  to  children,  even  if  no 
bacteria  are  present.  The  greatest  harm,  however,  is 
done  by  the  bacteria.  In  the  phlegmonous  form  of  inter- 
stitial mastitis  the  presence  of  fever  and  other  constitu- 
tional disturbances  renders  the  milk  unsuitable  for  food ; 
there  is  also  the  possibility  that  the  parenchyma  of  the 
udder  may  at  any  time  become  affected  and  the  causative 
bacteria  would  then  be  eliminated  in  the  milk. 

Therefore,  when  a  cow  is  affected  with  mastitis,  the 
milk  should  not  be  used  for  food  and,  if  possible,  the  cow 
should  be  removed  from  the  milk  stable  until  the  udder 
returns  to  the  normal  condition.  Cows  affected  with 
infectious  streptococcic,  septic,  or  gangrenous  mastitis 
should  always  be  isolated.  When  infectious  streptococcic 
mastitis  is  present  in  a  herd  it  may  be  necessary  to  pro- 
hibit the  use  of  any  of  the  milk  for  food  unless  it  is 
boiled  or  pasteurized,  but  even  then  such  milk  should 
not  be  used  for  children. 


INFLUENCE  OF  DISEASE  UPON  MILK  113 

BLOOD  IN  MILK 

&  mixture  of  blood  with  the  milk  may  occur  as  a 
result  of  traumatisms  of  the  udder,  such  as  kicking,  hook- 
ing or  treading,  which  cause  hemorrhages  or  blood  infil- 
trations into  the  udder  tissue.  The  pulling  or  dragging 
to  which  a  greatly  distended  udder  is  subjected  when  the 
cow  walks  may  cause  a  tearing  of  the  udder  tissue  which 
will  permit  the  mixing  of  blood  with  the  milk.  When 
large  blood  vessels  have  been  injured  the  milk  is  colored 
diffusely  red.  But  when  small  vessels  are  torn  or  rup- 
tured, which  is  more  often  the  case,  only  small  streaks  of 
blood  are  observed  which  disappear  when  the  milk  is 
shaken  and  do  not  discolor  it.  When  such  milk  is  centri- 
f  ugalized,  the  sediment  shows  a  red  color  which,  on  micro- 
scopic examination,  is  found  to  be  due  to  the  presence 
of  red-blood  cells.  Blood  is  observed  in  the  colostrum 
or  milk  during  the  first  week  following  parturition  in 
those  cases  in  which  the  udder  is  intensely  hypersemic, 
resulting  in  a  diapedesis  of  red-blood  cells. 

(EDEMA  OF  THE  UDDER 

Sometimes,  especially  in  heifers  with  the  first  calf, 
the  udder  becomes  very  much  swollen  and  oedematous 
shortly  before  parturition.  The  swelling  is  not  hot,  nor 
is  it  painful  unless  the  skin  is  intensely  stretched;  it 
disappears  a  few  days  after  parturition.  Usually,  no 
essential  changes  are  observed  in  the  milk.  It  is  probable 
that  some  of  the  serous  transudate  is  mixed  with  the 
milk,  but  nothing  definite  is  known  on  this  point.  Some- 
times the  milk  contains  blood.  Generally,  the  oedema 
has  disappeared  by  the  time  the  colostral  stage  is  passed. 
8 


114        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

INDIGESTION 

When  the  digestive  functions  of  the  dairy  cow  are 
disturbed,  as  in  gastro-intestinal  catarrh,  there  is  not 
only  a  decrease  in  the  quantity  of  milk  secreted,  but  quite 
frequently  the  milk  has  a  bitter  or  salty  taste  and  coagu- 
lates prematurely  (six  to  eight  hours  after  milking) .  It 
contains  less  fat  than  normal  milk  and  sometimes  appears 
thinner  and  of  a  yellow  color.  Milk  from  cows  in  this 
condition  may  possess  irritant  properties  and  when  in- 
gested unmixed  with  the  milk  of  other  cows  may  produce 
diarrhoea,  especially  in  children. 

The  milk  may  undergo  similar  changes  in  other  in- 
ternal diseases  which  do  not  directly  involve  the  udder. 

Spoiled  Feed. — The  milk  of  cows  fed  on  mouldy, 
fermented,  or  putrefied  feed  has  produced  diarrhoea  in 
persons  ingesting  it.  This  effect  has  been  attributed  to 
the  elimination  in  the  milk  of  abnormal  substances  con- 
tained in  such  feeds,  but  it  is  possible  that  the  organisms 
causing  the  changes  in  the  feed  may  have  gained  access 
to  the  milk  during  milking  and  caused  changes  in  the  milk 
itself  which  brought  on  the  diarrhoea. 

SEPTIC  OR  HEMORRHAGIC  ENTERITIS 
This  disease  consists  of  a  severe  or  bloody  diarrhoea 
associated  with  a  high  temperature  and  other  constitu- 
tional disturbances.  It  may  occur  sporadically  or  en- 
zootically,  especially  among  young  cattle.  According  to 
Jensen,  it  is  caused  by  bacteria  of  the  paracolon  group 
which  circulate  in  the  blood  and  which  are  also  present 
in  large  numbers  in  the  fecal  discharges.  Secondary  in- 
fection of  the  milk  during  milking  is  almost  certain  to 
occur  since  the  udder,  thighs,  and  flanks  of  the  diseased 
animal  will  be  soiled  by  the  fecal  matter.  The  bacteria, 


INFLUENCE  OF  DISEASE  UPON  MILK  115 

having  entered  the  blood  stream,  may  also  be  excreted 
in  the  milk  when  hemorrhages  have  occurred  in  the  udder 
tissue.  Two  instances  are  reported  in  which  milk  from 
cows  affected  with  this  disease  has  produced  disease  in 
man.  One  individual  was  affected  with  diarrhoea,  weak- 
ness, and  headache,  while  the  other  exhibited  symptoms 
resembling  typhoid  fever.  Cows  affected  with  a  severe 
or  bloody  diarrhoea  or  with  a  diarrhoea  associated  with 
fever  should  be  removed  from  the  milk  stable,  since  they 
are  likely  to  infect  not  only  their  own  milk  but  also  the 
milk  of  other  cows  with  pathogenic  bacteria.  The  stable 
should  be  cleaned  and  disinfected. 

SEPTIC  METRITIS 

In  acute  septic  metritis,  the  milk  secretion  usually 
ceases  with  the  sudden  onset  of  the  fever  and  the  animal 
generally  dies  in  a  few  days,  so  that  the  question  of  using 
the  milk  does  not  often  have  to  be  considered.  In  the 
less  acute  cases,  a  large  amount  of  chocolate-colored  fluid, 
which  is  frequently  putrid,  is  excreted  from  the  uterus 
and  soils  the  tail,  inner  surface  of  the  thighs,  and  udder, 
as  well  as  the  bedding,  stall,  and  suroundings.  This  fluid 
may  contain  staphylococci,  streptococci,  bacilli  of  the 
colon  and  paratyphus  groups,  and  putrefactive  bacteria. 
These  organisms  may  enter  the  milk  during  milking. 
The  milk  of  such  animals  usually  gives  a  positive  reac- 
tion to  the  alcohol  test,  indicating  that  some  of  the  prod- 
ucts of  the  disease  are  absorbed  from  the  uterus  and 
eliminated  through  the  udder.  The  foul  odor  of  the 
uterine  discharges  and  the  odor  of  antiseptics  which  may 
be  used  in  the  treatment  of  such  cows  will  be  absorbed 
by  the  milk.  While  no  cases  of  disease  in  man  from  the 
use  of  milk  from  cows  affected  with  septic  metritis  have 


116        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

been  reported,  there  is  no  doubt  that  the  milk  is  injurious 
to  health  because  numerous  cases  of  meat  poisoning  are 
on  record  from  the  use  of  meat  from  cows  slaughtered 
while  suffering  from  this  condition.  Cows  affected  with 
septic  metritis  should  therefore  be  removed  from  the  milk 
stable  and  the  milk  should  not  be  used  for  food. 

RETAINED  PLACENTA 

Following  retention  of  the  placenta,  there  is  a  dis- 
charge from  the  uterus  which  frequently  contains  par- 
ticles of  the  fetal  membranes  and  cotyledons  which  are 
undergoing  putrefaction,  also  pus,  pyogenic  organisms, 
and  putrefactive  bacteria.  The  tail,  thighs,  and  udder 
become  soiled  with  the  discharges  and  the  milk  may  be 
contaminated  during  milking.  In  cases  where  the  milk 
has  been  centrif  ugalized  and  the  sediment  examined  micro- 
scopically, large  numbers  of  staphylococci  and  diplococci 
have  been  found.  The  milk  will  also  give  a  positive  re- 
action to  the  alcohol  test,  indicating  that  the  secretion  is 
not  normal.  Milk  from  cows  with  a  purulent  or  putrid 
vaginal  discharge  should  not  be  used  for  food  purposes. 
Such  cows  should  not  be  placed  in  the  milk  stable 
until  the  condition  disappears,  as  there  is  a  possibility  of 
the  discharge  contaminating  the  milk  of  the  other  cows. 

INFECTIOUS  ABORTION 

The  milk  of  cows  which  have  aborted  contains  the 
Bacillus  abortus  Bang  very  frequently,  in  some  cases  for 
months  after  the  abortion.  Immediately  before  and 
for  several  weeks  after  abortion,  the  bacillus  is  also  elimi- 
nated through  the  vagina  and  may  infect  the  milk  second- 
arily. When  the  placenta  is  retained,  the  vaginal  dis- 
charge also  contains  pyogenic  and  putrefactive  organ- 


INFLUENCE  OF  DISEASE  UPON  MILK  117 

isms.    At  the  time  of  abortion  the  udder  secretion  fre- 
quently assumes  the  characteristics  of  colostrum. 

When  injected  into  guinea  pigs  or  fed  to  them,  milk 
containing  the  abortion  bacillus  produces  proliferative 
changes  similar  to  those  caused  by  the  tubercle  bacillus. 
The  organism  is  also  pathogenic  for  animals  of  several 
other  species.  This  widespread  pathogenicity  and  its 
frequent  occurrence  in  milk  suggested  the  desirability 
of  investigations  to  determine  if  the  organism  was  con- 
cerned in  the  sclerotic  changes  occurring  in  the  organs 
and  tissues  of  man  and  the  domestic  animals.  Mohler 
and  Traum  inoculated  guinea  pigs  with  material  from 
twenty-eight  tonsils  and  adenoids  from  milk-consuming 
children.  The  material  from  two  of  the  tonsils  produced 
lesions  in  three  guinea  pigs,  but  the  Bacillus  abortus  was 
recovered  only  from  the  lesions  in  one  of  these  animals. 
Whether  the  organism  was  actually  responsible  for  the 
change  in  the  tonsil  or  whether  it  merely  happened  to 
be  lodged  on  the  surface  could  not  be  determined. 
Schroeder  also  made  a  number  of  similar  tests,  all  with 
negative  results.  Mohler  tested  the  blood  serum  of 
twenty-five  persons  with  the  complement  fixation  and 
agglutination  tests  and  obtained  negative  results  in  all 
cases,  while  Larsen  and  Sedgwick,  in  applying  the  com- 
plement fixation  test  to  the  blood  serum  from  425  chil- 
dren, obtained  73  positive  reactions  (17  per  cent.). 
Ramsey  tested  the  blood  of  116  children  in  the  same 
manner,  but  the  reaction  was  positive  in  only  seven  cases. 
Nicholl  and  Pratt  obtained  positive  reactions  with  the 
agglutination  test  on  the  blood  serum  of  several  children. 
No  definite  statement  can  be  made  as  to  whether  the  anti- 


118        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

bodies  responsible  for  these  positive  reactions  were 
present  because  the  individuals  from  which  the  blood 
samples  were  obtained  had  actually  passed  through  some 
form  of  disease  due  to  the  abortion  bacillus  or  whether 
they  were  the  results  of  a  passive  immunity  due  to  the 
ingestion  of  milk  containing  the  bacillus  or  its  antibodies. 
But  it  has  been  demonstrated  in  a  number  of  experiments 
that  after  the  ingestion  of  an  organism  in  large  num- 
bers the  specific  antibodies  may  be  present  in  the  blood 
without  the  organism  producing  disease,  and  there  is 
some  reason  to  believe  that  antibodies  contained  in  the 
milk  may  be  absorbed  by  the  blood  from  the  intestinal 
canal  of  children  (see  page  43).  However,  there  is 
no  definite  information  that  abortion  bacilli  in  milk  have 
any  injurious  effect  upon  the  health  of  individuals  in- 
gesting such  milk. 

OTHER  DISEASES 

Any  disease  of  the  dairy  cow  attended  with  a  con- 
siderable disturbance  of  the  general  condition  usually 
causes  a  decrease  or  a  complete  cessation  of  the  milk 
secretion.  Although  the  milk  is  generally  of  normal 
appearance  when  secretion  continues  in  such  cases,  it 
frequently  contains  an  increased  amount  of  mineral  salts, 
has  a  salty  taste  and  coagulates  prematurely.  While  it 
is  not  known  that  milk  of  this  kind  is  harmful  to  man, 
the  change  in  its  composition  is  sufficient  to  justify  its 
condemnation  as  a  food. 

When  suppurating  wounds  or  ulcerative  or  phleg- 
monous  inflammations  are  present  in  any  part  of  the 
body,  there  is  danger  of  the  milk  being  infected  with  the 
pyogenic  organisms. 


INFLUENCE  OF  DISEASE  UPON  MILK  119 

EXCEETION  OF  MEDICINES  THROUGH  THE  UDDER 
A  number  of  medicines  used  in  the  treatment  of  dis- 
eased conditions  in  cattle  are  eliminated  in  part  through 
the  udder,  namely:  iodine,  mercury,  lead,  copper,  anti- 
mony, arsenic,  salicylic  acid,  antipyrin,  boric  acid,  aloes, 
rhubarb,  senna,  croton  oil,  euphorbium,  morphine,  strych- 
nine, atropine  and  veratrin.  Although,  under  ordinary 
conditions,  these  substances  are  eliminated  in  the  milk 
in  small  quantity,  there  is  a  possibility  that  milk  from 
cows  being  treated  with  these  drugs  may  be  injurious  to 
children  and  weak  adults.  When  elimination  through 
the  normal  channels  is  retarded  by  disease,  they  may  be 
eliminated  through  the  udder  in  larger  quantity,  and  sub- 
stances which  are  not  usually  excreted  through  the  udder 
may  also  pass  out  with  the  milk.  For  this  reason  milk 
should  not  be  used  for  food  from  a  cow  which  is  being 
treated  with  medicines  that  are  poisonous.  Aloes,  rhu- 
barb and  senna  affect  the  taste  and  color  of  milk. 

III.  DISEASES  OF  MAN  TRANSMISSIBLE  THROUGH  MILK 
Milk  may  act  as  a  carrier  of  the  bacteria  or  virus  of 
certain  specific  diseases  of  man.  From  time  to  time, 
epidemics  in  which  the  infectious  agent  has  been  dissemi- 
nated by  milk  have  been  reported,  particularly  outbreaks 
of  typhoid  fever,  septic  sore  throat,  diphtheria,  and  scarlet 
fever.  These  milk-borne  epidemics  have  certain  char- 
acteristics by  which  they  may  be  recognized,  viz :  1.  The 
epidemic  is  explosive  in  character,  a  large  number  of  cases 
occurring  at  about  the  same  time,  followed  later  by  a 
rapid  decrease  in  the  number  of  new  cases.  2.  The  dis- 
ease is  limited  to  those  families  receiving  their  milk  supply 
from  a  certain  distributer;  occurs  in  families  using  the 
greatest  amount  of  milk  and  affects  those  individuals 


120        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

using  the  most  milk,  generally  women  and  children.  3. 
The  period  of  incubation  is  relatively  short.  4.  The  dis- 
ease is  of  mild  type.  5.  The  mortality  is  lower  than  usual. 
As  a  rule,  the  conclusion  that  the  disease  is  dissemi- 
nated by  milk  must  be  based  upon  these  characteristics 
and  upon  information  obtained  regarding  the  manner  in 
which  the  milk  may  have  been  infected,  rather  than  upon 
the  demonstration  of  the  infectious  agent  in  the  milk. 
The  cause  of  scarlet  fever  is  not  known  and  consequently 
its  presence  cannot  be  detected  by  any  known  method  of 
examining  milk.  The  bacillus  of  typhoid  fever  has  been 
demonstrated  in  milk  several  times,  thus  affording  posi- 
tive proof  that  this  organism  is  transmitted  by  milk,  but 
the  examination  has  been  unsuccessful  in  a  much  larger 
number  of  cases.  The  diphtheria  bacillus  has  been  re- 
covered from  milk  in  even  fewer  instances.  There  are 
several  reasons  why  efforts  to  isolate  these  organisms 
from  milk  which  is  the  cause  of  an  epidemic  may  be  unsuc- 
cessful. 1.  Only  a  small  quantity  of  the  milk,  a  drop  or 
two,  is  subjected  to  examination,  and  this  may  be  free 
from  the  organisms  even  when  the  latter  are  relatively 
numerous  in  the  whole  volume  of  milk  concerned.  2.  The 
period  during  which  the  milk  is  infected  may  be  termi- 
nated before  it  is  suspected  and  examined.  3.  The  or- 
ganisms may  be  overgrown  by  the  other  kinds  of  bacteria 
which  are  present  in  milk  in  greater  number.  In  prac- 
tice, the  presence  of  these  infectious  agents  in  milk  is 
not  suspected  until  several  cases  of  disease  have  appeared. 
Even  if  they  could  be  detected  in  milk  with  more  cer- 
tainty, it  would  be  a  mistake  to  defer  action  after  an 
epidemic  has  started  until  the  milk  can  be  examined, 
because  this  would  allow  more  time  for  the  dissemination 
of  the  infection. 


INFLUENCE  OF  DISEASE  UPON  MILK  121 

TYPHOID  FEVER 

Typhoid  fever  is  more  frequently  spread  by  milk  than 
any  of  the  other  infectious  diseases  of  man  except  tuber- 
culosis. As  a  carrier  of  typhoid  infection,  milk  is  second 
only  to  water,  although  the  cases  caused  by  infected  water 
greatly  outnumber  those  resulting  from  infected  milk. 
Milk  may  be  infected  with  the  Bacillus  typhosus  in  sev- 
eral ways.  The  organisms  may  be  introduced  into  milk 
when  infected  water  is  used  to  wash  the  milk  vessels  and 
utensils.  Infected  water  may  contaminate  the  milk  when 
there  is  a  leak  in  the  milk  cooler  or  when  a  can  of  milk 
is  submerged  in  such  water  to  cool.  Water  in  open  or 
thin- walled  springs,  surface  wells,  and  in  streams  receiv- 
ing surface  drainage  may  be  readily  infected  by  excre- 
tions from  typhoid  fever  patients,  convalescents,  and 
chronic  bacilli  carriers.  Milk  bottles  from  houses  where 
the  disease  exists  may  be  a  source  of  infection;  one  or 
two  infected  bottles  may  contaminate  the  water  in  which 
they  are  washed  or  rinsed,  and  this  water  will  infect  other 
bottles  washed  in  it.  A  few  bacilli  introduced  into  a 
vessel  or  bottle  by  infected  water  will  multiply  rapidly 
when  milk  is  placed  in  it,  for  the  Bacillus  typhosus  grows 
abundantly  in  milk.  Milk  may  be  infected  directly  when 
the  cows  are  milked  or  the  milk  or  milk  vessels  are  handled 
by  persons  affected  with  the  disease,  by  convalescents, 
by  chronic  bacilli  carriers,  and  by  those  attending  typhoid 
fever  patients.  The  greatest  danger  of  direct  infection 
is  from  those  cases  in  which  the  disease  is  of  such  a  mild 
type  that  it  is  not  recognized,  the  so-called  walking 
typhoid,  and  from  chronic  bacilli  carriers,  i.e.,  individuals 
who  continue  to  excrete  typhoid  bacilli  in  the  faeces  and 
urine  after  they  have  recovered  from  the  disease.  It  is 
estimated  that  2  to  4  per  cent,  of  typhoid  fever  patients 


122         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

become  chronic  bacilli  carriers.  The  bacilli  may  also  be 
carried  by  flies  and  be  blown  about  in  dust. 

The  typhoid  bacillus  multiplies  rapidly  in  milk  and 
the  number  may  be  greatly  increased  in  a  short  time.  The 
milk  is  not  changed  in  appearance.  The  organism  grows 
in  slightly  sour  milk;  it  is  checked  or  destroyed  by  a  high 
degree  of  acidity,  but  it  survives  the  degree  of  acidity 
existing  in  cream  ripe  for  churning.  It  may  live  in  milk 
several  days  and  may  be  present  in  fresh  butter  and  new 
cheese.  Bruck  found  virulent  bacilli  in  butter  after 
twenty-seven  days.  Typhoid  bacilli  in  milk  are  destroyed 
when  exposed  to  a  temperature  of  60°  C.  (140°  F.)  for 
two  minutes  (Rosenau). 

When  an  outbreak  of  typhoid  fever  occurs  which  has 
the  characteristics  of  a  milk-borne  epidemic,  the  sus- 
pected milk  supply  should  be  stopped,  or  pasteurized 
under  supervision,  and  an  investigation  made  with  the 
object  of  discovering  and  abolishing  the  source  of  the 
infection  of  the  milk.  Immediate  medical  attention  to 
cases  of  illness  affecting  the  dairyman,  his  employees,  or 
members  of  their  households,  proper  supervision  of  cases 
of  typhoid  fever  by  health  authorities,  the  sterilization  of 
milk  bottles  before  refilling,  and  a  pure  water  supply  will 
greatly  reduce  the  liability  of  the  occurrence  of  such  epi- 
demics. There  is  no  method  known  which  is  entirely 
satisfactory  in  preventing  the  direct  infection  of  milk  by 
walking  typhoid  cases  or  by  chronic  bacilli  carriers. 
Recently,  some  local  health  authorities  have  required  that 
blood  samples  be  taken  from  dairy  employees  and  sub- 
mitted to  the  Widal  test  as  a  safeguard  against  chronic 
bacilli  carriers ;  a  few  high-class  dairies  have  been  follow- 
ing this  plan  for  some  time.  Several  states  have  laws 
requiring  dairymen  to  report  to  the  local  health  author- 


INFLUENCE  OF  DISEASE  UPON  MILK  123 

ities  all  cases  of  typhoid  fever  and  other  infectious  dis- 
eases occurring  in  their  own  families  and  among  their 
employees  or  in  the  families  of  the  latter. 

PARATYPHOID  FEVER 

Paratyphoid  fever  is  also  transmitted  by  milk,  but 
less  frequently  than  typhoid  fever.  The  milk  may  be 
infected  directly  with  the  paratyphus  bacilli  by  contact 
with  persons  affected  with  the  disease  or  indirectly  by 
polluted  water  being  used  to  wash  the  milk  vessels,  uten- 
sils, and  bottles.  Water  may  be  contaminated  by  fecal 
matter  from  infected  persons. 

DIPHTHERIA 

A  number  of  milk-borne  epidemics  of  diphtheria  are 
on  record,  although  this  disease  has  been  less  frequently 
disseminated  by  milk  than  typhoid  fever.  The  diph- 
theria bacilli  are  present  in  the  oral  cavity  and  on  the 
nasal  mucous  membrane  of  persons  affected  with  the 
disease  and  may  persist  in  these  locations  for  months 
after  the  patient  has  apparently  recovered.  Persons 
who  have  attended  diphtheria  patients  may  also  carry 
the  bacilli.  Infected  persons  may  infect  the  milk  directly 
or  indirectly.  In  the  beginning  of  some  cases  of  diph- 
theria, the  throat  is  apparently  normal  or  only  slightly 
affected.  These  cases  and  cases  of  chronic  nasal  diph- 
theria are  most  difficult  to  diagnose  from  clinical  symp- 
toms. Because  of  the  occurrence  of  cases  of  this  type 
and  the  continuance  of  the  bacilli  in  some  individuals 
after  the  subsidence  of  clinical  symptoms,  it  is  not  possible 
to  guard  entirely  against  the  occasional  infection  of  milk 
by  the  diphtheria  bacillus.  But  the  danger  will  be  greatly 
reduced  if  prompt  attention  is  given  to  all  cases  of  sore 


124        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

throat  occurring  among  dairy  workers  or  in  their  fam- 
ilies; if  persons  who  have  attended  diphtheria  patients 
or  individuals  recovering  from  the  disease  are  not  per- 
mitted to  handle  milk  or  milk  vessels  until  cultures  from 
the  throat  prove  to  be  free  from  the  bacilli,  and  if  re- 
turned bottles  are  sterilized  before  refilling.  Frequently 
the  bacilli  are  not  very  virulent. 

The  diphtheria  bacillus  has  been  demonstrated  in 
milk  only  a  few  times,  principally  because  the  organism 
is  present  in  infected  milk  in  small  numbers  and  usually 
for  only  a  short  period.  There  is  no  doubt,  however,  of 
its  transmission  by  milk.  The  milk  is  not  changed  in 
appearance  by  the  growth  of  the  organism.  The  bacillus 
is  not  affected  by  the  degree  of  acidity  present  in  cream 
ripe  for  churning,  and  it  may  therefore  be  present  in 
butter  and  also  in  other  dairy  products,  although  we  have 
no  reports  of  the  latter  carrying  infection.  A  compara- 
tively low  degree  of  heat  is  sufficient  to  destroy  the 
organism.  It  is  usually  killed  by  a  temperature  of  55°  C. 
(131°  F.),.but  occasionally  some  individuals  survive 
until  the  temperature  reaches  60°  C.  (140°  F.). 

When  an  outbreak  of  diphtheria  occurs  with  the 
characteristics  of  a  milk-borne  epidemic,  the  same  pro- 
cedure should  be  followed  as  described  under  typhoid 
fever. 

SEPTIC  SORE  THROAT 

Epidemics  of  septic  sore  throat  originating  from  in- 
fected milk  have  been  reported  from  England  for  a 
number  of  years  and,  in  recent  years,  several  outbreaks 
of  the  disease,  affecting  thousands  of  persons,  have  oc- 
curred in  this  country.  In  some  instances  the  infection 
of  the  milk  was  traced  to  cows  affected  with  streptococcic 


INFLUENCE  OF  DISEASE  UPON  MILK  125 

mastitis,  but  in  other  cases  there  seemed  to  be  reason  to 
suspect  that  the  milk  had  been  infected  by  persons  af- 
fected with  septic  sore  throat  (see  page  111) . 

SCARLET  FEVER 

Scarlet  fever  has  been  disseminated  by  milk  more 
rarely  than  some  of  the  other  infectious  diseases  of  man. 
The  epidemics  reported  occurred  principally  in  the 
United  States  and  England.  The  infectious  agent  of 
this  disease  has  not  been  discovered  and  it  is  not  definitely 
known  how  it  gains  access  to  milk,  but  it  is  presumed 
that  the  milk  is  infected  directly  or  indirectly  by  persons 
affected  with  the  disease.  The  same  action  should  be 
taken  against  a  milk-borne  epidemic  of  this  disease  as  is 
indicated  under  typhoid  fever. 

TUBERCULOSIS 

Tubercle  bacilli  of  the  human  type  have  been  demon- 
strated in  milk  (Hess,  Rabinowitsch),  and  there  would 
seem  to  be  abundant  opportunity  for  milk  to  be  infected 
by  a  consumptive  working  in  a  dairy.  Tuberculous 
individuals  should  therefore  not  be  permitted  to  handle 
milk. 


CHAPTER  VII 

DAIRY  FARM  INSPECTION 

THE  hygienic  qualities  of  milk  depend  very  largely 
upon  the  conditions  existing  at  the  source  of  supply.  A 
knowledge  of  these  conditions  can  be  obtained  only  by  an 
inspection  of  the  dairy  farm.  Collecting  a  sample  of  milk 
in  the  city  or  town  and  examining  it  in  the  laboratory 
will  disclose  certain  conditions,  and  it  will  usually  be  cor- 
rect to  infer  that  the  same  conditions  exist  in  the  entire 
volume  of  milk  from  which  the  sample  was  taken.  Some 
of  these  conditions  may  be  dangerous  to  the  health  of 
the  milk  consumer,  but  the  milk  will  have  been  consumed 
before  they  have  been  discovered.  Determining  the 
number  of  bacteria  per  c.c.  in  a  sample  of  milk  will  fur- 
nish a  good  basis  for  judging  the  care  observed  in  pro- 
ducing and  handling  the  milk,  especially  in  regard  to 
cleanliness  and  cooling,  but  it  will  not  discover  the  pres- 
ence of  the  bacilli  of  typhoid  fever,  tuberculosis,  or  diph- 
theria, nor  other  important  pathogenic  organisms.  Even 
if  it  were  practicable  to  subject  each  sample  of  milk  to 
the  comprehensive  examination  necessary  to  discover 
these  organisms,  the  milk  from  which  the  sample  was 
taken  would  be  consumed  long  before  the  examination 
could  be  completed.  It  is  more  rational  to  guard  the 
milk  against  contamination  at  the  source  than  to  attempt 
to  discover  contaminated  milk  after  it  reaches  the  city 
and  then  exclude  it  from  the  supply. 

While  it  may  not  be  possible  to  discover  the  actual 
contamination  of  the  milk  in  all  cases  by  inspecting  the 
dairy  farm,  the  conditions  which  permit  or  favor  con- 
126 


DAIRY  INSPECTION  127 

tamination  can,  with  few  exceptions,  be  discovered  by  a 
careful  inspection.  A  proper  laboratory  examination  of 
the  milk  in  connection  with  the  inspection  will  generally 
detect  those  conditions  which  may  escape  discovery  at 
the  inspection.  The  information  obtained  by  inspection 
will  serve  as  a  basis  for  judging  the  quality  of  milk  which 
may  be  produced,  not  only  on  the  day  of  inspection  but 
also  thereafter.  Moreover,  inspection  brings  a  repre- 
sentative of  the  health  authorities  into  personal  contact 
with  the  dairyman,  a  condition  which  should  make  for  a 
better  understanding  and  more  sympathy  on  both  sides. 
It  is  sometimes  asserted  that  the  bacterial  testing  of 
milk  is  more  efficient  in  improving  or  controlling  a  milk 
supply  than  dairy  inspection.  This  statement,  however, 
will  not  bear  critical  examination.  The  ordinary  bac- 
terial test  merely  approximates  the  number  of  clumps  of 
bacteria  present  in  a  very  small  portion  of  milk.  It  does 
not  determine  the  number  of  bacteria  present,  the  kind, 
nor  their  source.  It  does  not  tell  whether  a  high  count 
is  due  to  conditions  existing  at  the  dairy  farm,  during 
transportation,  or  at  the  distributing  plant.  It  does  not 
discover  the  presence  of  pathogenic  organisms,  excepting, 
perhaps,  streptococci,  and  it  does  not  indicate  the  source 
of  these  latter  organisms.  On  the  other  hand,  inspection 
of  a  dairy  farm  will  disclose  the  physical  condition  of  the 
cows,  the  sanitary  condition  of  the  premises,  the  char- 
acter of  the  equipment,  the  methods  in  use,  and  the  physi- 
cal condition  and  proficiency  of  the  dairyman  and  his 
employees.  Dairy  inspection  alone  will  certainly  furnish 
more  useful  information  for  judging  the  hygienic  prop- 
erties of  milk  than  bacterial  testing  alone.  As  an  ad  j  unct 
to  dairy  inspection,  however,  bacterial  testing  and  other 
laboratory  methods  of  examining  milk  are  of  great  ser- 


128        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

vice.  Unless  bacterial  testing  is  to  be  used  only  to  find 
faults  and  no  assistance  is  to  be  offered  in  correcting 
them,  it  must  be  combined  with  dairy  inspection. 

Inspection  of  a  dairy  farm  should  include  an  exami- 
nation of  the  following: 

I.  Stable: 

1.  Exterior. 

2.  Interior. 
II.  Cows: 

1.  Cleanliness. 

2.  Stage  of  lactation. 

3.  Symptoms  of  disease. 

III.  Stable  practices : 

1.  Cleaning  the  stable. 

2.  Cleaning  the  cows. 

3.  Milking. 

4.  Feeding. 

5.  Bedding. 

IV.  Milk  House: 

1.  Location. 

2.  Construction. 

3.  Apparatus. 

4.  Water  supply. 

A  certain  system  or  routine  should  be  followed  in 
making  the  inspection  so  that  nothing  will  be  overlooked. 
It  is  usually  convenient  to  begin  with  the  stable  and  then 
to  follow  the  course  of  the  milk  from  here  to  the  storage 
cans  or  bottles,  although  the  point  of  beginning  will  have 
to  be  varied  to  suit  the  circumstances.  The  best  time  to 
make  an  inspection  is  while  the  cows  are  being  milked, 
but,  unfortunately,  all  dairies  cannot  be  visited  at  this 
particular  time.  The  inspector  should  provide  himself 


DAIRY  INSPECTION  129 

with  a  suit  of  thin,  washable  material  to  protect  his 
clothing,  and  should  also  wear  a  close-fitting  cap  to  pro- 
tect his  hair  while  ausculting  the  lungs.  Material  of  blue 
or  a  darker  color  is  more  desirable  than  white,  because  in 
stables  where  white  suits  are  not  worn  by  the  milkers 
some  of  the  cows  are  likely  to  kick  at  a  stranger  wearing 
white  clothing.  The  inspection  should  be  carried  out  as 
follows : 

I.    STABLE 

1.  Exterior. — On  approaching  the  stable,  the  inspector 
should  take  note  of: 

(a)  The  location  of  the  building  with  regard  to  sur- 
face drainage.  It  is  desirable  to  have  the  floor  of  the 
stable  about  eight  inches  above  the  surrounding  ground 
and  to  have  the  adjoining  ground  slope  away  from  the 
stable. 

(6)  The  type  of  stable  and  its  general  construction 
— whether  a  bank  barn  with  the  stable  in  the  basement 
and  storage  space  above  for  feed,  or  a  one-story  stable 
entirely  above  the  ground ;  also,  whether  the  building  is 
constructed  of  stone,  wood,  or  cement.  Information  on 
these  points  may  be  of  value  later  in  the  inspection  in 
considering  the  arrangements  for  lighting  and  ventila- 
tion. 

(c)  Exposure. — The  direction  in  which  the  windows 
and  doors  face  is  of  importance,  as  it  has  considerable  in- 
fluence on  the  temperature  and  lighting  of  the  interior. 
When  there  can  be  windows  and  doors  on  only  one  side 
of  the  stable  it  is  best  to  have  them  facing  the  south. 
This  exposure  will  permit  the  morning  sun  to  shine  into 
the  stable  and  will  keep  out  the  hot  afternoon  sun  in 
summer  and  the  cold  winds  in  winter.  When  the  cows 
stand  in  a  double  row  the  most  desirable  arrangement 

9 


130        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

is  to  have  the  windows  on  the  east  and  west  sides  with  the 
two  rows  of  cows  extending  north  and  south.  The  win- 
dows on  the  west  side  can  be  provided  with  wood  shutters 
to  keep  out  the  sun  on  hot  summer  afternoons.  When 
the  shutters  are  up  the  flies  will  also  be  less  troublesome 
on  that  side  of  the  stable. 

(d)  Surroundings. — The  location  of  the  manure 
dump  and  the  direction  of  the  surface  drainage  from 
the  same  should  be  observed,  particularly  with  relation 
to  the  location  of  the  source  of  the  water  supply.  The 
accessibility  of  the  manure  pile  to  cows  turned  out  for 
exercise  or  being  driven  into  or  out  of  the  stable  should 
also  be  considered.  When  cows  are  permitted  to  wander 
about  in  a  lot  of  manure  they  become  very  much  soiled, 
especially  their  legs  and  udders,  and  also  carry  a  good 
deal  of  dirt  into  the  stable. 

The  proximity  of  other  buildings,  especially  if  used 
as  horse  stables,  chicken  houses,  pigpens,  etc.,  should  be 
noted.  Buildings  used  for  these  purposes,  as  well  as 
manure  piles,  are  breeding  places  for  flies  and  are  there- 
fore objectionable  when  too  close  to  a  dairy  stable  or  milk 
house. 

Attention  should  be  given  to  the  condition  of  the 
barnyard  or  exercise  yard.  Note  its  size  and  whether  or 
not  it  is  well  drained.  The  condition  of  the  barnyard 
has  a  considerable  effect  upon  the  cleanliness  of  the  cows 
and  stable.  If  it  is  muddy  or  dirty,  some  of  this  material 
will  become  attached  to  the  cows  and  will  be  carried  into 
the  stable,  increasing  the  labor  of  cleaning  the  cows  and 
the  stable. 

2.  Interior  of  the  Stable. — In  examining  the  cow  stable, 
the  fact  should  be  kept  in  mind  that  it  is  not  only  a  shelter 
for  animals  but  is  also  a  place  where  human  food  is  pro- 


DAIRY  INSPECTION  131 

duced.  Cows  in  milk  should  not  be  kept  in  the  same 
stable  with  horses  or  other  animals;  they  should  have  a 
separate  stable  for  their  exclusive  use.  There  should  be 
a  special  stable  for  parturition  and  for  cows  which  are 
not  in  health. 

(a)  Odor  of  the  Air. — On  entering  the  stable  the 
odor  of  the  air  should  be  noted,  since  any  slight  abnor- 
mality will  be  more  perceptible  at  this  time  than  later, 
when  the  inspector  has  become  accustomed  to  the  atmos- 
phere. The  odor  of  the  air  is  a  good  test  of  the  efficiency 
of  the  ventilation  and  also  of  the  degree  of  cleanliness 
of  the  stable,  especially  in  cold  weather  when  the  doors 
and  windows  are  closed  and  the  cows  are  kept  in  the 
stable  almost  continuously.  Abnormal  odors  in  stable 
air  usually  originate  from  two  sources :  exhalations  from 
the  cows  and  decomposing  manure  and  urine.  Condensa- 
tion of  moisture  on  the  walls,  ceiling,  or  windows  or  the 
presence  of  frost  is  another  indication  of  defective  venti- 
lation. A  moist  atmosphere  assists  in  the  spread  of  tuber- 
culosis in  a  stable.  The  droplets  of  infected  saliva  ex- 
pelled by  tuberculous  cattle  in  the  act  of  coughing  float 
more  readily  in  the  stable  air  when  it  is  saturated  with 
moisture  than  when  it  is  drier.  In  most  instances  cattle 
are  infected  with  tuberculosis  by  the  inhalation  of  in- 
fected air  or  by  the  ingestion  of  infected  food  or  water. 
Insufficient  ventilation  has  the  effect  of  concentrating  any 
infection  in  the  air  of  a  stable,  while  ventilation  dilutes  it. 

Recent  experiments  have  shown  that  the  harmf  ulness 
of  insufficient  ventilation  is  not  due  to  a  deficiency  of 
oxygen,  an  excess  of  carbon  dioxide,  or  the  presence  of 
organic  poisons  in  expired  air,  but  to  the  warmth  and 
moisture  of  the  air  in  unventilated  places  and  to  its  lack 
of  movement.  A  warm,  moist  atmosphere  has  a  depress- 


132        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

ing  effect  upon  the  animal  organism.  It  decreases  the 
working  capacity  of  the  muscles  and  lowers  the  vaso- 
motor  tone.  It  also  causes  a  congestion  of  the  nasal 
mucous  membrane,  rendering  the  animal  more  suscep- 
tible to  respiratory  infection.  There  is  also  reason  to 
believe  that  metabolism  is  depressed.  A  moderately  cool 
and  moderately  dry  air  in  motion  is  the  most  healthful 
atmosphere  for  animal  life. 

Ventilation. — The  best  system  of  ventilation  for  dairy  stables 
is  the  one  devised  by  the  late  Prof.  F.  H.  King.  Like  other 
systems,  it  has  inlets  for  the  admission  of  fresh  air  and  outlets 


FIG.  9. — Showing  on  the  left  how  an  inlet  can  be  placed  in  a  wall  already  constructed; 
on  the  right,  how  an  inlet  can  be  put  in  a  wall  being  built;  and  in  the  centre,  an  outlet  shaft 
with  two  openings — one  just  under  the  ceiling  and  one  a  foot  above  the  floor. 

for  the  removal  of  impure  air,  but  it  has  two  features  which  are 
peculiar  to  it.  The  inlet  flues  are  bent  at  a  right  angle,  and 
the  outside  opening  is  lower  than  the  inner  one,  the  purpose 
being  to  prevent  the  escape  of  air  from  the  stable  through  the 
inlets.  The  outlet  flues  are  built  from  the  floor  up  and  have 
an  opening  near  the  floor  as  well  as  one  near  the  ceiling,  thus 
providing  a  means  of  drawing  air  not  only  from  the  upper 


DAIRY  INSPECTION  133 

part  of  the  stable,  but  also  from  the  lower.  Inlets  are  placed 
in  all  of  the  outer  walls  of  the  stable  if  possible,  with  the  inside 
opening  just  under  the  ceiling  and  the  outside  opening  five  feet 
lower  (Fig.  9). 

The  number  and  size  of  inlets  necessary  will  vary  with 
weather  conditions,  and  it  is  therefore  desirable  to  have  as 
many  as  possible  and  then  use  as  many  as  may  be  needed. 
Weather  conditions  exert  considerable  influence  on  the  air  in 
stables  ventilated  by  any  system  which  depends  for  its  opera- 
tion on  natural  forces.  When  the  atmosphere  is  still  or  moist, 
the  ventilation  is  often  inefficient  in  stables  which  under  other 
conditions  are  well  ventilated. 

A  cow  requires  59  cubic  feet  of  air  per  minute  and  it  is 
estimated  that  air  will  pass  through  a  flue  at  the  rate  of  290 
to  300  feet  per  minute.  The  minimum  number  and  size  of 
inlets  and  of  outlets  required  may  therefore  be  calculated  accord- 
ing to  the  following  formula :  * 

No.  cows  in  stable  x  59  x  J44  gq  in    =  Total  cross-sectional  area  in  square  inches 
300  of  inlets  and  of  outlets. 

By  dividing  the  total  cross-sectional  area  by  the  number  of 
inlets  and  of  outlets,  the  cross-sectional  area  of  each  inlet  and 
outlet  is  ascertained.  The  number  of  inlets  and  of  outlets  will 
depend  upon  the  size  of  the  stable.  Inlets  should  not  be  over 
12  feet  apart ;  closer  if  possible.  Several  outlet  flues  of  moder- 
ate size  in  different  parts  of  the  stable  are  preferable  to  one 
or  two  large  outlets. 

Each  inlet  should  be  provided  with  a  sliding  door  or  other 
contrivance  by  which  it  can  be  conveniently  opened  or  closed. 
The  outlet  flues  should  extend  from  the  floor  to  6  feet  above 
the  highest  point  of  the  roof  and  should  be  capped  with  a  hood 
1  foot  above  the  top.  If  they  cannot  be  placed  where  they  will 
not  act  as  obstructions,  they  may  be  hinged  at  the  ceiling  so  that 
they  can  be  drawn  up  out  of  the  way  temporarily  (Fig.  10). 
Each  outlet  flue  should  have  two  openings  into  the  stable,  one 
just  under  the  ceiling  and  the  other  a  foot  above  the  floor,  both 
openings  being  provided  with  doors  which  can  be  readily  opened 

1  Wisconsin  Exp.  Sta.,  Bull.  No.  266. 


134        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

or  closed.  The  outlet  flues  must  be  air-tight  and  protected 
against  cold  in  exposed  places.  The  best  material  for  the 
construction  of  these  flues  is  galvanized  iron  (No.  28),  2  x  4 
inch  lumber  being  used  in  the  corners  and  joints.  Where  the 
shaft  is  exposed,  the  iron  should  be  covered  with  %-inch  boards. 
Outlets  may  also  be  constructed  of  a  double  layer  of  tongued 
and  grooved  boards  with  a  layer  of  heavy  building  paper  be- 
tween. If  tin  or  galvanized  iron  pipes  are  used,  they  should 
be  surrounded  by  a  square  wood  frame  and  the  interstices  filled 


FIG.  10. — An  outlet  flue  hinged  at  the  ceiling  so  that  it  can  be  drawn  up  out  of  the  way. 

in  with  sawdust.  Protection  against  cold  is  necessary  because 
the  air  in  the  outlet  flue  must  be  kept  warm,  otherwise  it  will 
cease  to  ascend.  The  ceiling  and  walls  of  the  stable  should  be 
air-tight  and  should  be  constructed  with  a  view  to  preventing 
the  radiation  of  heat  as  much  as  possible. 

The  circulation  of  air  through  the  stable  results  from  the 
operation  of  two  factors,  called  by  Professor  King  aeromotive 
forces,  namely:  heat  generated  by  the  cattle,  and  wind.  The 
wind  drives  air  through  the  inlets  on  the  windward  side  of  the 
stable  and  thus  increases  the  air  pressure  within  the  stable,  as  a 
result  of  which  air  is  forced  out  of  the  stable  through  the  outlets. 


DAIRY  INSPECTION  135 

If  the  wind  is  very  strong,  air  may  also  be  forced  out  through 
the  inlets  on  the  leeward  side,  but  ordinarily  the  right-angled 
bend  in  the  inlets  and  the  position  of  the  outer  opening  at  a 
lower  level  than  the  inner  prevents  or  retards  the  escape  of 
air  through  these  inlets.  In  addition,  wind  passing  over  the 
top  of  an  outlet  shaft  produces  a  suction  action  within  the  flue, 
and  this  draws  air  out  of  the  stable.  The  force  of  this  suction 
action  increases  with  the  height  of  the  outlet  shaft,  because 
air  movement  or  wind  increases  in  velocity  with  the  distance 
about  the  ground. 

The  heat  given  off  by  the  animals  in  the  stable  through 
the  skin  and  in  the  respired  air  warms  the  stable  air  around  them, 
expanding  it  and  decreasing  its  density  or  weight,  which  causes 
it  to  rise  toward  the  ceiling.  Fresh  air  entering  through  the 
inlets,  being  colder  and  heavier  than  the  air  in  the  stable,  gravi- 
tates toward  the  floor.  Through  the  operation  of  these  two 
currents  the  stable  air  and  fresh  air  are  mixed,  the  fresh  air 
is  warmed  while  the  stable  air  is  cooled  and  the  moisture  it 
contains  is  diluted.  However,  when  the  respired  air  is  cooled 
below  81°  F.,  it  becomes  heavier  than  fresh  air  of  the  same 
temperature  because  of  the  carbon  dioxide  which  it  contains  and 
consequently  settles  toward  the  floor.  For  this  reason,  it  is 
desirable  to  have  the  outlet  flues  arranged  to  draw  air  from 
the  lower  as  well  as  the  upper  part  of  the  stable.  The  expansion 
of  the  air  in  the  stable  by  the  animal  heat  increases  the  pressure 
within  the  stable  and  this  has  the  effect  of  forcing  air  through 
the  outlets;  the  construction  of  the  inlets  prevents  air  from 
being  forced  out  through  them.  To  obtain  satisfactory  results, 
the  air  in  the  stable  should  be  about  20°  F.  warmer  than  the  air 
outside.  The  effect  of  temperature  differences  on  the  draft  in 
outlet  flues  increases  with  the  length  of  the  flue.  The  resistance 
encountered  by  air  in  passing  through  inlets  and  outlets  modifies 
to  some  extent  the  effects  of  wind  and  heat.  It  is  therefore 
desirable  to  have  the  outlet  flues  as  straight  as  possible. 

Cloth  Method  of  Ventilation. — Stables  may  be  ventilated  by 
covering  windows  with  muslin  or  cheese  cloth.  Glass  windows 
should  be  alternated  with  the  cloth-covered  windows  in  order  to 
permit  sufficient  light  to  enter  the  stable.  Three  square  feet 


136        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

of  glass  and  2  square  feet  of  cloth  for  each  1000  pounds  of 
animal  weight  is  a  good  proportion.  When  the  air  is  still,  a 
stable  ventilated  by  means  of  muslin-covered  windows  will  not  be 
more  than  1  to  3°  F.  colder  than  stables  in  which  the  King 
system  is  used,  and  there  will  be  7  to  10  per  cent,  less  humidity 
in  the  stable  air ;  but  when  high  winds  prevail,  the  animal  heat 
will  be  rapidly  dissipated  and  the  stable  will  be  colder.  If  the 
cloth  becomes  wet  and  freezes,  ventilation  will  cease. 

(b)  Cubic  Air  Space. — This  is  determined  by  meas- 
uring the  length  and  width  of  the  stable,  multiplying  the 
length  by  the  width,  and  then  multiplying  the  result  thus 
obtained  by  the  height  of  the  ceiling.  After  the  total 
cubic  feet  of  air  space  has  been  ascertained  in  this  manner, 
the  stanchions  or  ties  should  be  counted  and  the  total 
cubic  feet  of  air  space  divided  by  the  number  of 
stanchions.  The  result  will  be  the  cubic  feet  of  air  space 
per  animal.  The  number  of  stanchions  or  ties  should  be 
used  for  this  purpose  instead  of  the  number  of  animals 
present  because  this  method  will  give  the  minimum  cubic 
feet  of  air  space  per  animal  under  all  conditions. 

The  size  of  a  stable  in  proportion  to  the  number  of 
animals  in  it  bears  an  important  relation  to  ventilation. 
The  less  air  space  per  animal  the  more  frequently  the 
air  in  the  stable  must  be  changed.  The  heat  given  off  by 
animals  is  only  sufficient  to  warm  a  certain  quantity  of 
air,  and  if  this  limit  is  exceeded  the  stable  will  be  cold  in 
winter.  A  stable  with  insufficient  cubic  air  spaces  will  also 
be  hot  and  uncomfortable  in  summer. 

It  is  desirable  to  have  1  cubic  foot  of  air  space  for 
each  pound  of  animal  weight,  but  this  amount  cannot 
always  be  provided  because  of  the  cost  of  building  mate- 
rials and  for  other  reasons.  With  suitable  arrangements 
for  ventilation,  500  to  600  cubic  feet  of  air  space  per  cow 


DAIRY  INSPECTION  137 

will  answer  quite  well.    A  cow  requires  59  cubic  feet  of 
air  per  minute,  or  3540  cubic  feet  per  hour.    To  provide 
this  amount  for  a  cow  occupying  a  space  of  500  to  600 
cubic  feet,  it  would  be  necessary  to  entirely  change  the 
air  in  the  space  occupied  by  the  cow  six  to  seven  times 
per  hour.    It  is  estimated  that  the  heat  given  off  by  a 
cow  in  24  hours  is  equal  to  76,133  British  thermal  units, 
which  is  sufficient  to  heat  79,603  cubic  feet  of  dry  air 
from  0°  to  50°  F.    This  quantity  of  air  would  provide 
3316  cubic  feet  of  air  per  hour,  only  224  cubic  feet  less 
than  the  quantity  required  by  the  cow.1    It  would  appear, 
therefore,  that  the  required  amount  of  fresh  air  could 
be  admitted  to  a  stable  with  500  to  600  cubic  feet  of  air 
space  per  cow  without  lowering  the  temperature  too 
much,  especially  since  the  temperature  only  rarely  falls 
to  0°  F.  in  the  dairy  sections  in  the  northern  part  of  the 
United  States.    The  most  comfortable  temperature  for 
the  dairy  cow  is  from  60°  to  65°  F.,  but  if  the  temperature 
is  kept  lower  by  ventilation,  say  down  to  50°  F.,  the  cow 
will  not  suffer  in  health  and  the  milk  flow  will  not  be 
reduced,  provided  exposure  to  the  low  temperature  be- 
gins in  the  autumn  and  is  continuous.    Milk  cows  have 
been  kept  through  the  winter  in  sheds  open  to  the  south 
with  quite  satisfactory  results. 

The  distribution  of  the  cubic  air  space  is  important. 
If  the  ceiling  is  too  high,  the  stable  is  likely  to  be  cold  at 
the  level  occupied  by  the  cows,  although  the  upper  part 
may  be  warm  enough.  The  height  of  the  ceiling  should 
be  regulated  by  the  size  of  the  stable.  Eight  feet  is  a 
sufficient  height  for  small  stables.  In  a  stable  for  12  cows 

1  These  figures  are  taken  from  Prof.  F.  H.  King's  book  on 
"  Ventilation." 


138        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

the  ceiling  should  not  be  over  10  feet  high;  for  30  cows, 
not  over  12  to  15  feet;  more  than  30  cows,  not  over  16 
feet  ( Rievel ) .  The  length  and  width  of  the  stable  should 
be  such  as  will  provide  sufficient  floor  space  to  accom- 
modate the  cows  comfortably  and  to  make  it  convenient 
to  milk  and  care  for  them.  When  the  cows  stand  facing 
the  centre  of  the  stable,  the  alley  or  passageway  in  back 
of  them  should  be  of  sufficient  width  to  permit  the  passage 
of  a  man  carrying  a  pail  of  milk  without  the  pail  touch- 
ing or  coming  too  near  the  cows.  To  meet  this  require- 
ment it  is  necessary  for  the  passageway  to  be  at  least 
3  feet  wide,  the  milk  pail  being  carried  on  the  side  of  the 
milker  farthest  from  the  cow,  but  a  width  of  5  or  6  feet 
is  much  better.  A  narrow  passageway  back  of  the  cows 
makes  it  difficult  to  keep  the  wall  clean.  The  passageway 
between  two  rows  of  cows  standing  tail  to  tail  should  be 
at  least  8  feet  wide;  it  can  hardly  be  wide  enough  to 
prevent  milk  carried  in  a  pail  between  the  cows  from  be- 
ing contaminated  by  the  dust  dislodged  by  the  switching 
of  the  tails.  There  is  also  danger  of  contamination  from 
splashing  urine  and  manure. 

To  provide  500  to  600  cubic  feet  of  air  space  per  cow 
the  floor  space,  with  a  9-foot  ceiling,  may  be  distributed 
as  follows: 

Feed  alley 4  feet 

Manger 1%  to  2  feet 

Platform 4%  to  5%  feet 

Gutter 16  inches 

Alley  in  rear  of  cows  5  to  6  feet 

The  total  of  these  dimensions  would  be  18  feet.  Al- 
lowing 3%  feet  for  the  width  of  the  stall,  there  would  be 
63  square  feet  of  floor  space  for  each  cow,  which,  with  a 


DAIRY  INSPECTION  139 

ceiling  9  feet  high,  would  provide  567  cubic  feet  of  air 
space  per  cow.  With  the  cows  standing  in  two  rows,  the 
stable  would  be  36  feet  wide,  which  is  not  too  wide  for  it 
to  be  well  lighted  if  windows  are  placed  on  both  sides. 
It  will  therefore  be  seen  that  the  necessary  area  of  floor 
space  to  make  the  cows  comfortable  and  the  stable  work 
convenient  will  also  provide  a  fair  amount  of  cubic  air 
space. 

(c)  Interior  Construction. — The  material  used  in 
the  construction  of  the  ceiling,  walls,  floor,  platform,  feed 
trough,  drop  or  gutter,  and  stall  fittings,  their  state  of 
repair  and  their  condition  in  regard  to  cleanliness  should 
be  noted.  While  defects  and  deficiencies  in  stable  con- 
struction may  be  overcome  to  a  considerable  extent  by 
careful  and  painstaking  methods,  at  the  same  time  a 
properly  constructed  and  conveniently  arranged  stable 
saves  labor  and  therefore  encourages  the  practice  of  good 
methods ;  it  also  adds  to  the  comfort  of  the  cows  and  con- 
sequently increases  their  productiveness. 

The  ceiling  should  be  tight  and  smooth,  plastered, 
painted,  oiled,  or  whitewashed,  and  free  from  cobwebs. 
There  is  no  objection  to  storing  hay  or  fodder  above  the 
cow  stable  if  the  ceiling  is  tight.  It  is  better  not  to  have 
any  openings  in  the  ceiling  through  which  hay,  fodder 
or  straw  may  be  thrown  down  into  the  stable;  but  if 
there  must  be  such  openings,  they  should  be  in  front  of 
the  cows  and  not  in  the  rear. 

The  walls  should  be  smooth  and  clean.  It  is  desirable 
to  have  the  inner  surface  of  the  walls  back  of  the  cows 
finished  smooth  with  cement  for  at  least  4  feet  above  the 
floor  and  covered  with  an  impervious  paint  from  which 
dirt  can  be  readily  removed  by  washing.  Where  paint  or 
cement  cannot  be  used,  the  application  of  whitewash  will 


140        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

improve  the  conditions.  Any  woodwork  can  be  treated 
in  the  same  manner.  Whitewashing  removes  dirt  and 
cobwebs,  improves  the  light,  and  exerts  a  disinfectant 
action. 

The  platform,  or  the  floor  of  the  stall,,  should  be  about 
8  inches  above  the  bottom  of  the  drop  or  gutter  and 
should  be  smooth,  free  from  cracks  or  depressions  and 
impervious.    All  things  considered,  cement  is  probably 
the   best   material    of   which   to    construct    platforms. 
Cement  platforms  are  objected  to  on  the  ground  that 
they  are  slippery,  cold,  and  hard.     If  given  a  rough 
finish  with  a  wood  trowel  or  by  drawing  a  stiff  broom 
over  the  surface  before  the  cement  is  dry,  they  will  not  be 
slippery.    A  layer  of  coal  tar  or  pitch  about  1%  inches 
below  the  surface  will  reduce  the  conduction  of  heat  from 
the  body  of  the  cow  and  will  therefore  make  the  platform 
warmer,  while  the  hardness  can  be  overcome  to  a  certain 
extent  by  the  use  of  plenty  of  bedding.     Recently,  a 
mixture  of  two  parts  of  sawdust  and  one  part  of  cement 
has  been  recommended  in  place  of  the  usual  cement  mix- 
ture, the  claim  being  made  that  it  is  warmer  and  is  not  as 
slippery.    A  covering  of  inch  boards  is  sometimes  laid 
down  over  the  cement  to  reduce  the  hardness  and  cold- 
ness.   Cement  floors  have  several  advantages:  they  are 
readily  cleaned,  wear  well,  and  do  not  absorb  urine  or 
liquid  manure  nor  permit  these  substances  to  leak  through 
and  saturate  the  earth  beneath.     Next  to  cement,  the 
most  desirable  floor  is  one  of  matched  planks,  with  the 
joints  filled  with  tar.    Wood  is  less  of  a  heat  conductor 
than  cement  and  is  not  as  hard,  but  it  absorbs  urine  and 
liquid  manure  and  is  liable  to  crack  and  form  crevices  in 
which  manure  and  other  material  may  lodge  and  decom- 
pose; it  is  also  less  durable  than  cement.     Cork  bricks 


DAIRY  INSPECTION  141 

laid  on  concrete  are  also  used  for  platforms  and  floors. 
It  is  claimed  for  them  that  they  combine  the  good  prop- 
erties of  cement  and  wood  and  at  the  same  time  do  not 
have  any  of  the  undesirable  properties  of  those  sub- 
stances. An  earth  floor  is  most  objectionable.  Unless 
plenty  of  good  absorbent  litter  is  used  it  is  very  likely 
to  be  wet  and  dirty;  it  finally  becomes  saturated  with 
urine  and  liquid  manure,  which  decompose  and  liberate 
foul-smelling  gases. 

The  rear  18  inches  of  the  platform  should  slope 
slightly  toward  the  gutter,  just  sufficient  to  cause  liquids 
to  flow  in  that  direction.  Too  much  slope  is  likely  to 
cause  the  cow  to  slip ;  it  also  causes  the  cow  to  stand  down 
in  the  gutter  and  favors  prolapse  of  the  vagina  and 
similar  troubles.  It  is  desirable  to  have  a  depression  in 
the  front  of  the  platform  %  inch  deep  and  extending 
back  about  18  inches  from  the  anterior  border.  This  will 
prevent  cows  from  falling  on  their  knees  when  attempt- 
ing to  rise  or  when  reaching  for  feed,  and  will  also  have 
a  tendency  to  keep  the  litter  from  being  pushed  toward 
the  rear  of  the  stall  (Fig.  11). 

The  length  of  the  platform  is  important ;  if  too  long, 
the  fasces  are  dropped  where  the  cow  can  lie  upon  them ; 
if  too  short,  the  cow  is  uncomfortable  and  stands  down 
in  the  gutter.  The  proper  length  is  4%  to  5%  feet, 
differing  with  the  size  of  the  cow.  Frequently,  where 
a  number  of  cows  stand  in  a  row,  the  platforms  are  made 
4%  feet  long  at  one  end  with  a  gradual  increase  to  5% 
feet  at  the  other  end  of  the  row,  thus  supplying  platforms 
of  different  lengths  on  which  the  cows  can  be  placed  ac- 
cording to  size.  The  platform  for  each  cow  should  be 
3%  to  4  feet  wide,  depending  upon  the  size  of  the  cow. 
The  width  is  quite  as  important  as  the  length,  because 


DAIRY  INSPECTION  143 

if  the  stall  is  too  wide  and  the  cow  stands  diagonally 
the  result  will  be  the  same  as  if  the  platform  was  too 
long.  The  stall  should  be  constructed  with  the  view  of 
preventing  the  dropping  of  manure  where  the  cow  can 
lie  down  upon  it,  in  so  far  as  this  is  possible,  and  thus 
save  labor  in  keeping  the  cow  clean.  Other  points  to 
be  considered  are  the  comfort  of  the  cow,  convenience  of 
cleaning  the  stall,  milking,  and  feeding,  and  the  cost. 

The  feed  trough  or  manger  may  be  built  of  wood  or 
cement.  Cement  is  better  because  it  is  easier  to  keep 
clean.  A  continuous  cement  trough,  extending  in  front 
of  a  row  of  cows  without  any  divisions,  can  also  be  used 
for  water.  In  addition,  the  continuous  trough  is  more 
conveniently  cleaned,  but  on  the  other  hand  it  favors  the 
spread  of  infectious  diseases,  especially  tuberculosis. 
Feed  placed  before  a  tuberculous  cow  may  be  contami- 
nated by  infected  saliva  and  material  ejected  in  cough- 
ing, after  which  it  can  be  readily  obtained  by  cows  in 
adjoining  stalls;  the  tuberculous  cow  may  also  contami- 
nate the  feed  of  the  cows  standing  on  either  side,  and  also 
of  cows  standing  opposite,  and  when  water  is  run  into 
the  trough  infection  may  be  carried  from  one  end  of  it 
to  the  other.  On  the  other  hand,  separate  feed  troughs 
or  mangers,  although  decreasing  the  danger  of  infec- 
tion, increase  the  labor  of  cleaning;  they  also  make  it 
necessary  to  have  individual  drinking  cups  or  to  drive 
the  cows  to  water  outside  of  the  stable.  When  a  herd  is 
regularly  tested  with  tuberculin  and  the  reactors 
promptly  removed,  and  when  the  trough  is  swept  and 
washed  daily,  the  danger  of  infection  from  the  common 
feeding  trough  is  greatly  reduced.  The  bottom  of  the 
feed  trough  should  be  2  inches  higher  than  the  level  of 
the  platform.  When  cows  have  to  reach  too  far  for  their 


144        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

feed,  the  front  feet  frequently  slip  backward  and  the 
cows  are  thrown  on  their  knees,  causing  bruises  which 
often  lead  to  the  development  of  knee  tumors.  The  feed 
trough  should  be  18  inches  wide  and  at  least  6  inches 
deep,  with  the  front  high  enough  to  prevent  feed  from 
being  pushed  out  of  it. 

The  gutter  or  drop  should  be  constructed  of  cement. 
Wood  or  earth  gutters  cannot  be  kept  clean  and  free 
from  odor.  The  gutter  should  be  16  to  18  inches  wide, 
with  an  average  depth  of  8  inches  below  the  level  of  the 
platform.  It  should  be  deeper  at  one  end  than  at  the 
other,  to  give  the  bottom  sufficient  slope  for  drainage, 
or  the  entire  floor  may  be  sloped  and  the  depth  of  the 
gutter  remain  the  same.  Sometimes  the  floor  back  of 
the  platforms  is  laid  on  a  level  with  the  bottom  of  the 
gutter  or  2  or  3  inches  above  it,  thus  removing  the  back 
wall  of  the  gutter  entirely  or  making  it  4  or  5  inches  lower 
than  the  front  wall.  This  has  the  advantage  of  per- 
mitting the  sun  to  shine  into  the  gutter  when  there  are 
windows  in  the  rear  of  the  cows,  but  it  also  increases 
the  likelihood  of  manure  being  splashed  upon  the  wall; 
when  the  back  wall  of  the  gutter  is  lacking  entirely  there 
is  a  tendency  for  the  hind  feet  of  cows  to  slip  backward 
when  they  are  stepping  up  onto  the  platform.  Plenty 
of  litter  should  be  kept  in  the  gutter  to  absorb  the  urine 
and  thus  prevent  it  from  being  splashed  by  droppings 
or  by  the  cow's  tail  when  the  animal  is  lying  down  and 
switching  at  flies.  The  floor  of  the  gutter  sometimes  has 
a  %  inch  slope  from  the  front  to  the  rear  with  the  object 
of  raising  the  toe  and  increasing  the  tension  upon  the 
posterior  tendons  when  cows  stand  down  in  the  gutter, 
the  intention  being  to  make  the  position  uncomfortable, 
but  this  construction  does  not  always  have  the  desired 
effect. 


DAIRY  INSPECTION  145 

Ties  or  Stanchions. — From  a  sanitary  standpoint, 
stanchions  or  jacks  are  better  than  chains  because  they 
are  more  likely  to  hold  the  cow  in  the  proper  place  in  the 
stall  to  cause  the  manure  to  be  dropped  into  the  gutter, 
thus  assisting  indirectly  in  keeping  the  cows  clean.  The 
swinging  chain-stanchion  is  also  quite  comfortable.  The 
best  material  for  stanchions  and  their  supports  is  metal 
piping. 

Stall  divisions  help  to  keep  the  cow  in  place  and  thus 
assist  in  keeping  the  platform  and  the  cow  clean;  they 
also  prevent  the  cow  from  treading  on  the  udder  or  teats 
of  a  neighboring  cow.  Solid,  board  partitions,  extending 
from  the  floor  upward,  are  objectionable  because  they 
increase  the  difficulty  of  keeping  the  stable  clean  and 
interfere  with  the  circulation  of  air ;  they  may  also  be  in 
the  way  of  the  milker.  Wood  fittings  with  flat  surfaces 
and  cracks  are  not  as  easily  kept  clean  as  round,  smooth 
surfaces,  and  the  cracks  make  disinfection  more  difficult. 
Stall  divisions  consisting  of  a  single  piece  of  metal  pipe, 
extending  in  a  curve  from  the  front  post  of  the  stall  to 
the  rear  of  the  platform,  with  a  radius  of  3  feet,  are  not 
open  to  these  objections. 

Arrangement  of  the  Stalls. — When  stalls  in  a  stable 
are  placed  in  two  rows,  they  are  arranged  with  the  cows 
in  one  row  facing  those  in  the  other,  with  the  feed  alley 
in  the  centre  between  the  mangers,  and  a  passageway  in 
the  rear  between  the  manure  gutter  and  the  side  wall ;  or, 
the  stalls  are  arranged  with  the  cows  in  each  row  facing 
outward  toward  the  side  walls,  with  a  feed  alley  in  front 
of  each  row  between  the  manger  and  the  wall  and  a  pass- 
ageway extending  through  the  middle  of  the  stable  be- 
tween the  two  rows  of  cows.  Both  plans  have  advan- 
tages and  disadvantages.  When  the  cows  stand  facing  a 
10 


146         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

central  feed  alley,  feeding  is  facilitated  and,  if  there  are 
windows  in  the  side  walls,  the  posterior  part  of  the  cow 
is  in  the  lightest  part  of  the  stable,  which  is  a  convenience 
in  cleaning  the  cow  and  in  milking;  but  the  spread  of 
infection  is  favored  because  material  coughed  out  by  one 
cow  may  be  deposited  in  the  feed  trough  of  the  cow 
standing  opposite  in  the  other  row.  With  the  cows  fac- 
ing outward  toward  the  side  walls,  the  cleansing  of  the 
stable  and  the  removal  of  the  manure  is  facilitated  and 
there  is  less  exposure  to  infection  by  coughing,  but  the 
cleaning  of  the  cow  and  the  milking  must  be  done  in 
the  darkest  part  of  the  stable  and  the  milk  must  also  be 
carried  between  the  two  rows  of  cows  and  is  thus  exposed 
to  external  contamination,  especially  in  the  fly  season 
when  the  cows  frequently  switch  their  tails. 

Maternity  and  hospital  stalls  should  be  provided  in 
another  part  of  the  building  or  in  another  building.  If 
there  are  not  special  stalls  for  these  purposes,  cows  with 
vaginal  discharge  from  retained  placenta  and  with  other 
pathological  excretions  will  be  stabled  in  the  milking  line 
and  may  infect  the  milk  indirectly. 

(d)  Light. — The  cow  stable  should  receive  sufficient 
daylight  to  make  it  possible  to  read  ordinary  newspaper 
print  in  the  middle  of  it.  This  much  light  is  necessary  for 
the  cleaning  and  the  milking  of  the  cows  to  receive  proper 
attention.  Nearly  all  of  the  work  which  must  be  done  in 
a  cow  stable  can  be  done  better  and  easier  in  the  light  than 
in  the  dark.  The  admission  of  sunlight  into  a  stable  is 
beneficial  in  several  respects.  It  lights  the  stable  and 
exposes  dirt,  thus  assisting  in  keeping  the  stable  and 
cows  clean;  it  facilitates  careful  milking;  assists  in  dry- 
ing out  the  stable ;  supplies  some  warmth  to  the  stable  in 
winter,  and  has  a  disinfectant  action.  The  germicidal 


DAIRY  INSPECTION 


147 


effect  of  sunlight  is  not  fully  appreciated.  Experiments 
with  artificial  cultures  of  various  bacteria  have  shown 
that  direct  sunlight  is  very  destructive  to  germ  life,  while 
the  action  of  diffused  light,  although  less  powerful,  is  also 
quite  effective.  Tubercle  bacilli  are  killed  by  direct  sun- 
light in  a  few  hours,  while  even  diffused  daylight  destroys 
them  in  a  few  days  (Koch) . 
Direct  sunlight  kills  anthrax 
spores  in  five  hours  and  the 
bacilli  in  thirty  hours,  spores 
being  more  susceptible  to 
sunlight  than  bacilli  (Ar- 
loing,  Roux).  Direct  sun- 
light destroys  or  decreases 
the  virulence  of  colon  bacilli, 
the  bacilli  of  fowl  cholera 
and  swine  erysipelas,  and  the 
virus  of  hog  cholera,  while 
diffuse  daylight  also  exerts 
a  similar  but  less  powerful 
action  (Neumark). 

The  inspector  should 
note  the  location  and  size  of 
the  windows  and  determine 
the  total  square  feet  of  win- 
dow surface.  He  should  Flo  12_windowarrangedtoactasafresh 
also  observe  whether  the  air  inlet  (Wis'  E*p' Sta' BulL  No' 266)' 
glass  is  clean  and  if  other  buildings  obstruct  the  en- 
trance of  light.  Three  to  four  square  feet  of  win- 
dow surface  for  each  cow  will  usually  admit  sufficient 
light,  provided  the  windows  are  properly  placed  and 
equally  distributed.  In  cold  climates,  an  excess  of  win- 
dow surface  may  increase  the  radiation  of  heat  to  such  an 


148        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

extent  as  to  interfere  with  ventilation;  this  can  be  avoided 
by  constructing  double  windows,  with  an  air  space  be- 
tween. Where  cows  stand  in  a  double  row,  a  row  of 
windows  along  each  side  of  the  barn  is  very  desirable. 
The  windows  may  be  hinged  at  the  bottom  and  arranged 
to  open  and  close  by  turning  a  continuous  rod ;  or  they 
may  be  unattached,  as  many  prefer,  and  merely  rest  in 
a  groove  in  the  window  sill,  being  held  in  place  by  a  peg 
near  the  top.  If  the  windows  are  to  be  used  as  inlets  for 
ventilation,  the  openings  formed  at  either  side  when  the 
sash  is  inclined  inward  at  the  top  should  be  closed  by 
boards  or  galvanized  iron  strips  extending  inward  from 
the  window  frame  on  each  side.  The  galvanized  iron 
shields  prevent  the  wind  from  entering  at  the  sides  and 
blowing  directly  upon  the  cattle  (see  Fig.  12). 

The  arrangements  for  artificial  lighting  should  be 
noted.  These  are  rather  important,  for  much  of  the  work 
in  the  stable  in  winter  is  done  before  and  after  daylight. 

II.    COWS 

The  examination  of  the  cow  is  one  of  the  most  impor- 
tant parts  of  dairy  inspection.  If  the  cows  are  not  in  the 
stable  at  the  time  of  the  inspector's  visit  and  if  it  is  not 
convenient  to  bring  them  in,  this  part  of  the  inspection 
should  be  made  at  a  more  opportune  time,  but  the  inspec- 
tion of  the  dairy  should  not  be  regarded  as  completed 
until  the  cows  are  examined.  No  attempt  should  be  made 
to  examine  the  cows  while  they  are  running  free  in  the 
pasture  or  exercise  lot,  unless  each  one  can  be  readily 
caught  and  handled. 

1.  Examination  for  Cleanliness. — Observe  the  condition 
of  the  cows  with  regard  to  cleanliness,  especially  the  con- 


DAIRY  INSPECTION  149 

dition  of  the  flanks  and  udder.  The  condition  of  the 
cows  in  this  respect  is  usually  an  indication  of  the  care 
they  receive  and  of  the  efforts  made  to  keep  the  milk 
clean.  It  is  not  necessary  for  the  inspector  to  be  present 
when  the  work  is  done  in  order  to  determine  if  the  cows 
are  regularly  cleaned.  When  cows  are  regularly 
groomed,  the  posterior  quarters  are  comparatively  free 
from  dried  manure  and  the  hair  coat  is  smooth  and  some- 
what glossy.  The  hair  is  also  shorter  and  thinner  than 
on  cows  which  are  not  regularly  brushed.  Clipping  the 
hair  short  on  the  udder,  flanks,  buttocks,  and  tail,  and 
cutting  three  or  four  inches  off  the  switch  if  it  touches  the 
floor,  is  of  great  assistance  in  keeping  the  cows  clean,  and 
evidence  of  clipping  is  an  indication  that  the  cows  are 
regularly  groomed.  Exfoliations  from  the  skin  and  par- 
ticles of  dirt  are  likely  to  collect  in  the  hollows  about  the 
root  of  the  tail  and  their  presence  in  any  great  quantity 
points  to  carelessness  or  neglect  in  cleaning.  Fresh 
manure  on  the  buttocks  (point  of  ischium)  is  not  neces- 
sarily an  indication  that  the  cow  was  not  properly  cleaned. 
These  parts  are  readily  soiled  if,  during  defecation,  the 
tail  is  pressed  down  on  the  faeces  and  is  subsequently 
moved  from  side  to  side. 

2.  Stage  of  Lactation. — Examination  and  inquiry 
should  be  made  regarding  the  stage  of  lactation.  The 
daily  milk  record,  if  available,  will  be  of  great  assistance 
in  discovering  cows  near  the  end  of  lactation.  When  the 
milk  flow  has  decreased  to  a  quart  (2  pounds)  a  day  or 
less,  the  milk  is  likely  to  have  a  salty  taste  or  a  strong, 
cow-like  odor  and  taste,  and  in  many  cases  the  cream  will 
not  "  butter."  Such  cows  should  be  "  dried  off."  The 
secretion  of  fresh  cows  should  be  examined  for  the  char- 
acteristics of  colostrum. 


150        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

3.  Examination  for  Symptoms  of  Disease.— This  exami- 
nation consists  of  two  parts:  (a)  General  examination 
and  (b)  special  examination. 

(a)    GENERAL  EXAMINATION 

The  general  examination  is  made  first,  with  the  cow 
in  the  stall.  Taking  a  position  in  the  rear  and  slightly 
to  one  side,  the  inspector  proceeds  with  the  examination 
in  the  following  order: 

1.  Attitude. — Note  the  general  appearance,  the  car- 
riage of  the  head,  position  of  the  ears  (erect  or  hanging) , 
standing  position,  behavior  (quiet  or  restless) . 

Dullness  or  depression  from  fever,  also  weakness  and  pain 
may  be  discovered  in  this  way.  Very  sick  animals  and  those 
with  a  high  fever  usually  hold  the  head  low,  with  the  ears 
drooping.  In  severe  vaginitis  and  metritis,  and  sometimes  in 
constipation  and  colic,  cows  stand  with  the  back  arched,  head 
lowered,  tail  elevated,  and  legs  spread  apart.  Sometimes  cows 
affected  with  vaginitis  stand  a  long  time  in  the  attitude  of 
urination.  An  arched  back  and  erect  hair,  in  association  with 
shivering  and  a  cold  skin  are  symptoms  of  fever,  although  they 
are  not  constant.  In  dyspnoea  and  sore  throat  the  head  is 
extended.  Pain  causes  restlessness ;  soreness  of  the  extremities 
is  indicated  by  resting  the  affected  limb,  or,  when  more  than  one 
limb  is  affected,  by  continually  shifting  the  body  weight  from 
one  leg  to  another.  Cows  often  lie  down  during  the  day,  espe- 
cially after  eating,  and  do  not  rise  on  the  approach  of  man; 
therefore,  a  recumbent  position  is  of  less  significance  with  these 
animals  than  in  the  case  of  the  horse.  A  disposition  to  lie  down 
continually  may  be  due  to  articular  rheumatism  or  to  osteo- 
malacia.  Inability  to  rise  is  caused  by  paralysis  (spinal  frac- 
tures), milk  fever,  and  ante  and  postpartum  paralysis.  Some- 
times refusal  to  rise  is  due  to  stubbornness. 

2.  Skin  and  Hear. — Observe  the  condition  of  the  skin 
and  hair  and  look  for  swellings,  enlargements  and  irregu- 
larities of  form. 


DAIRY  INSPECTION  151 

Rough,  bristling,  lustreless  hair  and  a  dry,  stiff  skin  (hide- 
bound) indicates  unthriftiness  or  lack  of  condition,  which  may 
be  due  to  disease  or  improper  care.  In  stables  in  which  the 
cows  are  regularly  groomed,  fresh  cows,  especially  heifers  with 
the  first  calf,  may  appear  rough  and  thin  in  comparison  with  the 
other  cows  for  a  week  or  two  after  they  are  placed  in  the  milk 
stable.  This  condition  is  due  to  the  effects  of  parturition  and 
to  not  being  regularly  groomed  previously ;  it  must  not  be  con- 
fused with  unthriftiness.  When  associated  with  a  good  appe- 
tite, unthriftiness  and  progressive  emaciation  are  indications 
of  chronic  disease,  frequently  of  tuberculosis.  Emaciation, 
however,  may  be  due  to  old  age.  Mere  thinness  must  not  be 
mistaken  for  unthriftiness  or  emaciation;  heavy  milking  cows 
are  often  thin.  The  condition  of  the  skin  and  hair  is  a  better 
indication  of  the  actual  physical  condition  than  the  degree  of 
fleshiness  or  leanness. 

Swellings  may  occur  in  or  beneath  the  skin  (local  inflamma- 
tions, oedemas,  abscesses,  enlarged  lymph  glands,  actinomycosis, 
etc.)  and  suppurating  wounds  may  involve  the  skin  and  sub- 
cutaneous structures.  Distension  of  the  left  side  of  the  abdomen 
occurs  in  impaction  and  tympanites  of  the  rumen. 

3.  Vulva,  Anus,  and  Tail. — These  should  be  ex- 
amined for  evidences  of  pathological  discharges.  Dis- 
eases of  the  uterus,  vagina,  and  digestive  tract  may  be 
discovered  in  this  way.  There  are  certain  normal  dis- 
charges from  the  vulva  which  must  not  be  mistaken  for 
pathological  discharges.  A  small  amount  of  glassy 
mucous,  frequently  blood-stained,  is  discharged  during 
oestrum;  a  bloody  or  grayish  albuminous  discharge  is 
sometimes  seen  after  breeding,  while  near  the  end  of 
pregnancy  there  is  usually  observed  a  glassy  mucous  dis- 
charge which  is  often  of  a  red  color. 

A  foul,  chocolate-colored  or  reddish  fluid  containing  frag- 
ments of  tissue  is  discharged  from  the  vulva  following  retention 
of  the  placenta.  In  metritis  and  vaginitis  the  discharge  is  either 


152        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

colorless  or  yellow,  red  or  chocolate  color,  thin  at  first  and 
gradually  becoming  thicker.  In  chronic  metritis  the  discharge 
is  white,  sticky,  and  odorless,  or  muco-purulent,  purulent,  or 
chocolate-colored  and  foul-smelling.  A  slight  purulent  dis- 
charge occurs  in  tuberculosis  of  the  uterus.  When  the  discharge 
is  slight  it  may  be  observed  only  when  the  cow  lies  down  or  its 
presence  may  be  indicated  only  by  a  soiled  condition  of  the  tail. 
The  vulva  is  swollen  in  metritis  and  in  puerperal  septicaemia. 
In  tuberculosis  of  the  uterus  the  vulva  is  flabby  and  the  broad 
ligaments  are  relaxed  and  sunken.  Relaxation  of  the  broad 
ligaments  also  occurs  in  ovarian  disease  and  frequently  in 
aged  cows. 

If  defecation  does  not  occur  during  the  examination  the 
character  of  the  bowel  discharges  may  be  determined  by  ex- 
amining the  manure  in  the  gutter  or  drop  and  by  observing  the 
condition  of  the  tail  and  buttocks.  Soft  bowel  discharges,  if 
general,  may  indicate  a  sudden  change  in  feed,  overfeeding,  or 
the  feeding  of  spoiled  feed,  as  well  as  disease.  Dry,  hard  faeces, 
often  of  a  darker  color  than  normal,  are  seen  in  constipation 
and  in  severe  febrile  disease ;  soft  or  semi-fluid  faeces  in  intestinal 
catarrh,  advanced  tuberculosis  of  the  mesenteric  lymph  glands, 
pseudo-tuberculosis  or  Johne's  disease  and  enteritis ;  red,  choco- 
late-colored or  black  faeces  in  hemorrhagic  enteritis  and  dysen- 
tery. Blood  is  present  in  streaks  or  clots  in  hemorrhage  of  the 
rectum  and  bloody  discharges  occur  in  anthrax.  Coarse  par- 
ticles of  food  in  the  faeces  indicate  disturbance  of  rumination  in 
consequence  of  impaction,  torpidity,  or  paralysis  of  the  rumen. 

4.  Respiration. — The  rate,  rhythm,  intensity,  and 
character  of  the  respiratory  movements  can  be  deter- 
mined by  observing  the  movement  of  the  flanks. 

Rapid  breathing  is  often  seen  in  advanced  pulmonary  tuber- 
culosis, but  it  is  not  a  constant  symptom.  The  rate  of  respira- 
tion is  increased  in  other  diseases  of  the  respiratory  tract,  in 
fever  and  in  painful  conditions.  An  increase  in  the  respiratory 
rate  occurs  also  immediately  after  eating,  after  exercise,  and  in 
hot  weather.  Increase  in  the  intensity  or  depth  of  the  respira- 


DAIRY  INSPECTION  153 

tory  movements  is  a  symptom  of  disease,  except  when  it  occurs 
after  exercise.  A  decrease  in  the  intensity  or  depth  (shallow 
respiration)  is  observed  in  pleurisy  and  in  painful  conditions 
of  the  chest  wall. 

5.  Udder. — Examine  the  udder  by  inspection.    This 
can  be  done  best  when  the  udder  is  full.    Compare  the 
form  and  size  of  the  different  quarters.    Look  for  swell- 
ing (mastitis),  atrophy,  furuncles  (feed  boils),  altera- 
tions of  cowpox,  etc. 

6.  Appetite. — Look  into  the  manger  and  see  if  the 
feed  has  been  eaten  and  note  if  the  animal  is  ruminating. 

7.  Muzzle  and  Nostrils. — Touch  the   muzzle   and 
determine  the  degree  of  temperature  and  moisture.    Ex- 
amine the  nostrils  for  pathological  discharges. 

The  muzzle  is  dry  and  sometimes  roughened  in  fever  and 
diarrhea.  It  is  alternately  hot  and  cold  in  fever,  and  cold  and 
dry  in  low  conditions  endangering  life.  Vesicles  occur  on  the 
muzzle  in  foot  and  mouth  disease. 

A  discharge  from  the  nostrils  occurs  in  exudative  diseases  of 
the  respiratory  tract,  but  in  tuberculosis  the  discharge  is 
frequently  not  present  because  the  exudate  is  usually  coughed 
up  and  swallowed.  A  nasal  discharge  may  escape  notice  in 
cattle  because  it  is  generally  licked  off  with  the  tongue.  It  is 
most  likely  to  be  seen  after  coughing.  A  slight  mucous  dis- 
charge is  normal. 

8.  Submcuvillary  and  Peripharyngeal  Regions. — At- 
tempt to  palpate  the  submaxillary,  parotid,  retropharyn- 
geal  and  atlantal  lymph  glands ;  they  cannot  be  felt  unless 
enlarged. 

The  submaxillary  lymph-gland  is  situated  within  the  pos- 
terior angle  of  the  lower  jaw,  between  the  sternocephalicus 
(sternomaxillaris)  muscle  and  the  submaxillary  salivary  gland. 


154        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

The  sub  parotid  lymph-gland  is  about  2~y2  inches  long,  flat 
and  tongue-like  in  form  and  is  located  just  under  the  anterior 
border  of  the  parotid  salivary  gland  and  about  3  inches  below 
the  base  of  the  ear.  In  feeling  for  this  gland  press  the  finger 
inward  and  backward  in  the  groove  between  the  posterior  border 
of  the  lower  jaw  and  the  parotid  salivary  gland. 

The  retropharyngeal  lymph-gland,  also  called  the  pharyn- 
geal  and  superior  pharyngeal,  is  about  2  inches  long  and  is 
situated  on  the  posterior  wall  of  the  pharynx.  It  can  be  pal- 
pated, when  enlarged,  by  pressing  the  extended  fingers  inward 
from  each  side  toward  the  median  line  and  as  far  forward  as 
possible  between  the  muscles  of  the  neck  and  the  larynx. 

The  atlantal  or  posterior  retropharyngeal  lymph-gland  is 
situated  under  the  wing  of  the  atlas,  partly  covered  by  the 
upper  end  of  the  submaxillary  salivary  gland.  By  pressing  the 
fingers  inward  and  upward  under  the  wing  of  the  atlas  this 
gland  is  forced  against  the  under  surface  of  the  wing  of  the 
atlas. 

When  any  of  these  glands  in  cattle  are  enlarged  and  firm 
and  not  hot  or  painful,  tuberculosis  is  usually  present.  En- 
largement of  the  retropharyngeal  glands  may  interfere  with 
swallowing  and  respiration. 

Actinomycotic  tumors  may  be  observed  in  the  submaxillary 
and  peripharyngeal  regions  as  well  as  in  the  maxillae  and  tongue. 

9.  Cough. — Test  each  cow  for  cough  by  exerting 
pressure  with  the  fingers  on  the  larynx  or  first  three 
rings  of  the  trachea,  or  close  both  nostrils  for  about  a 
minute;  also  grasp  the  skin  over  the  withers  with  the 
fingers  of  both  hands  and  draw  it  upward.  Take  note 
of  any  coughing  which  occurs  spontaneously  and  identify 
the  cow  each  time. 

A  frequent,  chronic  cough  is  one  of  the  most  prominent 
symptoms  of  pulmonary  tuberculosis.  If  a  cow  can  be  made 
to  cough  by  pinching  the  larynx  or  the  adjoining  rings  of  the 
trachea,  or  by  closing  the  nostrils,  it  is  an  indication  of  disease 
of  the  respiratory  tract.  Cough  can  usually  be  induced  in  this 


DAIRY  INSPECTION  155 

way  in  advanced  tuberculosis  of  the  lungs ;  if  the  cough  is  low, 
weak,  and  moist,  it  is  especially  suspicious.  Old  cows  are  not 
infrequently  affected  with  pulmonary  emphysema,  and  a  short, 
dry  cough  may  be  readily  induced  in  such  animals ;  but  even  a 
cough  of  this  character  is  suspicious  of  tuberculosis.  A  cow  in 
health  may  cough  as  a  result  of  inhaling  dust,  cold  air,  or  irri- 
tating gases,  but  the  cough  is  not  frequent  or  chronic.  Cough 
in  cattle  is  softer,  hollow  (toneless),  and  more  prolonged  than 
in  the  horse. 

If  drawing  the  skin  up  over  the  withers  produces  cough,  it 
is  an  indication  of  an  irritated  condition  of  the  lungs  or  pleura. 

10.  Lungs. — The  lungs  should  be  examined  by  aus- 
cultation.   In  doubtful  cases,  closing  the  nostrils  for  a 
short  time  or  exercise  will  render  the   sounds  more 
audible. 

Exaggeration  of  the  vesicular  murmur  (when  not  due  to 
exercise)  and  the  presence  of  the  bronchial  sound,  rales,  or 
vague  sounds  are  evidences  of  disease  of  the  bronchi  or  lungs. 
Friction  sounds  occur  in  pleuritis  (fibrinous).  In  tuberculosis, 
especially  after  exercise,  the  vesicular  murmur  may  be  exagger- 
ated and  rough,  and  rales  and  vague  sounds  may  be  heard.  The 
disease  may  exist,  however,  when  no  abnormal  sounds  can  be 
detected.  In  old  cows  sibilant  rales  may  be  heard  because  of  the 
presence  of  pulmonary  emphysema. 

11.  Prescapular   and   Precrural   Lymph-glands. — 
The  precrural  glands  can  be  palpated  whether  normal 
or  enlarged,  but  the  prescapular  glands  cannot  be  felt 
unless  they  are  enlarged. 

The  prescapular  lymph-gland,  also  called  the  superficial 
cervical,  is  situated  beneath  a  layer  of  muscular  tissue  at  the 
anterior  border  of  the  shoulder,  a  little  above  the  shoulder 
joint. 

The  precrural  lymph-gland  is  situated  in  the  flank,  just 
under  the  skin,  at  the  anterior  border  of  the  tensor  fasciae 


156         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

latse  muscle.     Normally,  it  is  about  1  inch  in  width  and  4  to  6 
inches  long. 

When  these  glands  are  enlarged,  firm  and  not  hot  or  painful, 
they  are  usually  tuberculous.  The  lymph-glands  are  also  en- 
larged in  leuksemia  and  pseudoleukaemia,  but  in  these  diseases  all 
of  the  superficial  lymph-glands  on  both  sides  of  the  body  are 
similarly  affected. 

12.  Complete  the  Examination  of  the  Udder  and 
Examine  the  Supramammary  Lymph-glands. — Inspect 
the  skin  of  the  udder  and  teats  for  furuncles,  ulcers, 
symptoms  of  cowpox,  etc.  Inspect  the  opening  of  the 
teat  canal  for  scabs. 

Palpate  the  udder.  This  is  done  most  satisfactorily 
when  the  udder  is  empty.  Beginning  with  the  inferior 
extremity  of  the  teat  and  passing  upward,  palpate  suc- 
cessively the  teat  canal,  the  milk  cistern,  the  gland  tissue 
and  the  supramammary  lymph-glands.  Note  the  tem- 
perature of  the  parts  and  look  for  symptoms  of  acute 
inflammation,  induration,  and  nodules.  By  rolling  the 
teat  between  the  fingers,  thickening  of  the  mucous  mem- 
brane of  the  cistern  and  nodular  formations  in  the  walls 
of  the  cistern  and  teat  canal  can  be  detected.  In  palpat- 
ing the  udder,  pass  one  hand  up  between  the  two  halves 
of  the  organ,  place  the  other  hand  on  the  external  surface 
and  then,  beginning  at  the  posterior  or  anterior  extremity, 
slowly  work  the  udder  tissue  between  the  fingers,  search- 
ing for  indurations,  retention  cysts,  etc. 

Draw  milk  from  each  quarter  into  the  palm  of  the 
hand  and  examine  it  for  color,  consistency,  flakes,  clots, 
etc.  In  doubtful  cases  collect  a  sample  for  further 
examination.  Press  the  end  of  the  teat  to  see  if  any 
mucus  or  pus  can  be  squeezed  out  of  the  teat  canal.  Ob- 
serve if  there  is  any  difficulty  in  expressing  the  milk  from 


DAIRY  INSPECTION  157 

the  teat  and  if  the  stream  is  split  or  deflected  from  the 
normal  direction. 

Palpate  the  supramammary  lymph-glands.  Stand- 
ing in  the  rear  of  the  cow,  press  the  hand  forward  along 
the  upper  and  posterior  margin  of  the  udder,  with  the 
thumb  on  one  side  of  the  median  line  and  the  fingers  on 
the  other,  and  grasp  the  glands  by  bringing  the  fingers 
and  thumb  together.  Ordinarily,  these  glands  are  about 
2  inches  in  diameter,  but  in  heavy  milkers  they  may  be 
larger. 

Pronounced  swelling,  excessive  heat,  and  pain  in  one  or  more 
quarters  of  the  udder,  with  marked  changes  in  the  milk,  are 
symptoms  of  parenchymatous  mastitis. 

Firm  nodules  which  are  neither  hot  nor  painful,  or  a  rather 
diffuse  induration  which  is  painless  and  without  heat,  in  one  or 
both  posterior  quarters,  with  enlargement  of  the  supramam- 
mary lymph-glands,  are  symptoms  of  tuberculosis  of  the  udder. 
There  is  no  apparent  alteration  of  the  milk  during  the  first 
stages  of  the  disease.  Indurated  areas  of  greater  or  less  extent 
result  also  from  parenchymatous  and  catarrhal  mastitis,  but 
they  are  not  accompanied  by  enlargement  of  the  lymph-glands, 
except  in  the  acute  stage. 

Enlargement  of  the  supramammary  lymph-glands  is  asso- 
ciated with  tuberculosis  of  the  udder  and  also  occurs  during 
acute  mastitis.  These  glands  may  be  enlarged  as  a  result  of 
tuberculous  infection  when  no  symptoms  of  the  disease  are 
apparent  in  the  udder. 

Difficulty  in  expressing  milk  from  the  teat  and  deflection 
or  division  of  the  milk  stream  are  early  symptoms  of  catarrhal 
mastitis.  If  pus  or  mucus  can  be  squeezed  out  of  the  teat 
canal,  catarrhal  mastitis  is  present.  A  scab  may  be  found  over 
the  opening  of  the  teat  canal  when  this  disease  exists,  although 
clots  or  flakes  of  dried  milk  are  sometimes  present  when  the 
udder  is  normal  except  for  some  defect  in  the  sphincter  ap- 
paratus of  the  teat.  The  milk  may  appear  unaltered  or  show 
only  slight  changes  when  these  symptoms  are  present. 


158        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

A  thick  cord-like  induration,  about  the  thickness  of  a  lead 
pencil,  extending  vertically  through  the  middle  of  the  teat,  is  a 
symptom  of  catarrhal  mastitis ;  also  nodular  indurations  in  the 
walls  of  the  teat  canal  and  milk  cistern.  Only  slight  alterations 
may  be  present  in  the  milk,  or  none  at  all. 

Atrophy  is  usually  a  symptom  of  an  existing  or  previously 
existing  catarrhal  mastitis.  Milk  from  the  affected  quarter 
may  contain  the  organism  responsible  for  the  condition  even 
when  it  shows  no  perceptible  changes. 

(For  the  changes  in  milk  occurring  during  udder  disease 
see  pages  105-110.) 

Firm,  nodular  swellings,  not  hot  or  painful,  situated  in  the 
superficial  parts  of  the  udder  tissue,  which  are  not  movable  and 
which  can  be  reduced  by  strong  pressure,  are  retention  cysts, 
formed  by  the  blocking  of  the  milk  ducts. 

(6)    SPECIAL  EXAMINATION 

The  character  of  the  special  examination  will  depend 
upon  the  information  obtained  during  the  general 
examination. 

If  fever  is  suspected  the  temperature  should  be  taken 
with  a  thermometer  and  an  examination  made  for  the 
other  symptoms  of  fever  (chill;  irregularity  of  the  sur- 
face temperature,  especially  of  the  extremities ;  accelera- 
ation  of  the  pulse  and  respiration,  loss  of  appetite,  depres- 
sion, albuminuria ) .  In  cattle  the  increase  in  temperature 
as  shown  by  the  thermometer  does  not  always  correspond 
to  the  degree  of  fever  indicated  by  the  other  symptoms. 

When  thoracic  disease  is  suspected  the  chest  wall 
should  be  percussed.  Areas  of  hepatization  and  solidifi- 
cation may  thus  be  discovered.  The  area  of  the  lungs 
of  cattle  which  can  be  percussed  is  limited,  however,  and 
unfortunately  tubercular  solidifications  usually  occur 
below  this  area.  Percussion  may  reveal  painful  condi- 
tions of  the  lungs  and  pleura  and  may  also  produce 
cough. 


DAIRY  INSPECTION  159 

If  tuberculosis  of  the  uterus  is  suspected,  the  sub- 
sacral,  sublumbar  and  internal  inguinal  lymph-glands 
should  be  palpated  per  rectum.  These  glands  are  en- 
larged, firm,  and  often  nodular  when  the  uterus  is  tuber- 
culous. The  mesenteric  lymph-glands  can  also  be 
examined  in  the  same  manner. 

Further  information  regarding  internal  conditions 
can  be  obtained  by  examining  the  sclerotic  conjunctiva 
and  the  mucous  membrane  of  the  cheeks.  These  mem- 
branes are  pale  in  tuberculosis  and  in  other  chronic  debili- 
tating conditions  which  lead  to  anaemia  and  hydrsemia; 
bluish-red  (cyanotic)  in  febrile,  respiratory,  and  cardiac 
diseases  and  in  conditions  which  interfere  with  the  en- 
trance of  air  into  the  lungs ;  brick-red  to  dark  red,  with 
the  blood-vessels  injected,  in  hypersemia  and  inflamma- 
tion of  the  brain  and  in  conditions  which  interfere  with  the 
return  of  venous  blood  from  the  head  to  the  heart  (pul- 
monary emphysema,  organic  heart  disease  and  cardiac 
weakness) ;  ecchymotic  in  anthrax,  severe  anaemia  and 
pernicious  anaemia,  and  yellow  in  icterus. 

When  symptoms  suspicious  of  tuberculosis  are 
present  and  no  definite  conclusion  can  be  reached,  the 
cow  should  be  tested  with  tuberculin. 

When  catarrhal  mastitis  is  suspected  and  a  definite 
diagnosis  cannot  be  made,  the  milk  should  be  examined 
by  the  catalase,  leucocyte,  or  alcohol  tests  and  micro- 
scopically, for  streptococci. 

Ill    STABLE  PRACTICES 

Attention  should  be  given  to  the  manner  in  which  the 
stable  is  cleaned,  when  and  how  the  cows  are  cleaned,  the 
methods  of  milking  and  of  caring  for  the  milk,  the  time 
of  feeding,  character  of  the  feed,  and  when  the  litter  is 
put  down  and  the  material  used. 


160        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

1.  Method  of  Cleaning  the  Stable. — If  manure  is 
allowed  to  collect  in  the  stable  the  cows  will  become  soiled 
and  odors  of  decomposing  manure  and  urine  will  per- 
meate the  stable  air  and  may  be  absorbed  by  the  milk. 
The  manure  should  be  removed  twice  daily  if  possible, 
being  taken  out  before  each  milking.  It  is  necessary  to 
complete  this  work  at  least  an  hour  before  the  cows  are 
milked  in  order  to  allow  time  for  the  air  to  become  free 
from  dust  and  odor  before  milking  is  begun.  When  the 
cows  must  be  milked  very  early  in  the  morning  it  is  not 
always  practicable  to  get  the  manure  out  of  the  stable 
an  hour  before  milking  time,  and  in  such  cases  it  is  better 
to  remove  it  after  the  cows  are  milked  and  fed.  Milk  of 
good  quality  can  be  produced  under  these  conditions.  If 
the  manure  is  not  hauled  immediately  to  the  fields,  it 
should  be  stored  as  far  away  from  the  stable  as  possible. 
The  stable  and  its  immediate  surroundings  should  be  kept 
as  free  as  possible  from  manure  and  other  decaying  or- 
ganic matter  because  flies  breed  in  such  material.  House- 
flies  may  travel  considerable  distances  from  where  they 
breed,  flights  of  one-quarter  to  nearly  a  mile  having  been 
observed,  but,  as  they  seem  to  be  attracted  by  odors,  keep- 
ing the  stable  clean  will  in  a  measure  serve  as  a  protec- 
tion when  flies  are  permitted  to  breed  in  the  neighbor- 
hood. 

After  the  manure  has  been  taken  out,  the  litter  on 
the  rear  end  of  the  platform,  which  is  usually  soiled, 
should  be  swept  into  the  gutter  and  given  an  opportunity 
to  absorb  any  liquid  which  may  be  present.  When  the 
cows  have  been  cleaned,  the  rear  end  of  the  platforms 
and  the  floor  back  of  the  gutter  should  be  sprinkled  with 
water  and  swept  clean.  In  some  stables  the  platforms 
and  floors  are  again  sprinkled  after  sweeping.  This  is 


DAIRY  INSPECTION  16r 

done  to  keep  the  atmosphere  as  free  from  dust  as  possible. 
In  other  stables  land  plaster  is  spread  in  a  thin  layer  on 
the  floor  and  in  the  gutter  to  act  as  an  absorbent.  This 
is  especially  desirable  when  the  floor  is  of  wood  or  earth. 
The  use  of  land  plaster  also  seems  to  have  the  effect  of 
reducing  the  number  of  flies.  Although  the  inspector 
cannot  be  present  during  all  of  these  operations,  he  can 
make  a  fairly  accurate  estimate  of  how  thoroughly  the 
work  is  done  by  observing  the  condition  of  the  stable 
at  the  time  of  his  visit.  Dirt  which  has  been  permitted 
to  remain  for  some  time  can  be  easily  distinguished  from 
fresh  dirt.  The  wall  in  the  rear  of  the  cows  and  the 
corners  formed  where  the  walls,  posts,  and  stall  divisions 
join  the  floor  should  be  especially  examined.  The  pres- 
ence of  cobwebs  on  the  walls,  ceiling,  or  other  places  is 
an  evidence  of  infrequent  sweeping. 

Flies. — The  presence  of  flies  in  large  numbers  in  and  about 
a  cow  stable  is  objectionable  for  several  reasons.  The  flies 
worry  the  cows  and  reduce  the  milk  production,  while  the  move- 
ments of  the  cows  in  their  efforts  to  protect  themselves  from 
the  insects  interfere  with  milking  and  are  also  likely  to  dislodge 
dirt  from  the  body  of  the  cow ;  some  of  this  dirt  may  fall  into 
the  milk  pail.  The  common  house-fly  (Muse a  domes tica)  is 
especially  objectionable.  It  feeds  upon  all  kinds  of  organic 
matter,  including  human  excrement,  and  becomes  contaminated 
with  numerous  bacteria.  A  single  fly  may  carry  over  a  million 
germs  on  the  surface  of  its  body.  When  it  feeds  upon  milk 
or  crawls  or  falls  into  milk  vessels,  many  of  these  bacteria  are 
transferred  to  the  milk.  Typhoid  bacilli  may  be  carried  from 
infected  fecal  matter  to  milk  in  this  way.  The  small,  black  cow- 
fly  or  horn-fly  (Hematobia  serrata,  Lyperosia  irritans  L.)  and 
the  stable-fly  or  biting-fly  (Stomoxys  calcitraws)  disturb  the 
cow  more  than  the  house-fly,  because  they  are  biting  or  blood- 
sucking insects;  but  they  do  not  as  a  rule  invade  the  milk 
vessels  or  the  milk. 
11 


162         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Various  methods  are  used  to  reduce  the  number  of  flies  in 
cow  stables  and  in  milk-houses.  The  cows  are  sprayed  or 
brushed  with  mixtures  of  drugs  or  chemicals  known  as  fly 
repellents.  Sometimes  sheets  of  fly-paper  are  placed  about  the 
buildings.  Milk-houses  are  very  often  screened  and  more  rarely 
stables  are  also  screened.  Fly  repellents  are  only  temporary 
in  their  action  and  they  are  often  objectionable  on  account  of 
their  odor.  Fly-paper  is  unsightly  and  inefficient.  Fly-traps 
are  more  useful.  Screening  milk-houses  gives  good  results  and 
is  desirable  in  all  cases,  but  screening  stables  is  not  satisfactory. 
Since  the  doors  must  be  opened  frequently  and  sometimes  for 
long  periods  to  remove  manure,  to  take  in  the  feed,  and  to  drive 
the  cows  in  and  out,  there  is  abundant  opportunity  for  flies 
to  enter.  The  cow-fly  or  horn-fly  is  carried  in  on  the  cows.  All 
of  these  methods  are  fundamentally  defective  because  none  of 
them  prevents  the  breeding  of  flies.  The  most  rational  method 
of  attacking  the  fly  problem  is  to  remove  or  abolish,  in  so  far  as 
is  possible,  the  conditions  which  favor  the  development  of  the 
insects.  To  do  this  intelligently  it  is  necessary  to  consider  their 
habits  and  life  history. 

Three  varieties  of  flies  are  commonly  found  in  cow  stables : 
the  common  house-fly,  the  cow-fly  or  horn-fly,  and  the  stable- 
fly  or  biting-fly.  The  house-fly  and  cow-fly  are  usually  the  most 
numerous,  but  in  some  sections  of  the  country,  especially  in  the 
grain  belt,  the  stable-fly  is  present  in  large  numbers.  The  dif- 
ferent varieties  can  usually  be  distinguished  by  the  part  of  the 
cow  which  they  occupy  and  by  their  sitting  position.  The  small, 
black  cow-fly  is  generally  located  upon  the  back  and  sides  of  the 
cow,  and  in  rainy  weather  on  the  under  parts  of  the  body,  sitting 
with  the  head  downward.  The  stable-fly  usually  occupies  the 
lower  parts  of  the  legs  and  nearly  always  sits  with  the  head 
upward,  while  the  house-fly  may  be  found  on  any  part  of  the 
cow  and  may  sit  in  any  position,  but  never  with  the  head  pressed 
into  the  hair  as  though  feeding.  The  stable-fly  is  about  the 
same  size  as  the  house-fly  but  has  a  more  plump  appearance 
and  has  longitudinal  lines  on  the  thorax  and  several  dark  spots 
on  the  abdomen.  The  horn-fly  is  smaller  and  black. 

The  house-fly  seems  to  prefer  to  deposit  its  eggs  in  horse 


DAIRY  INSPECTION  163 

manure,  but  when  this  is  not  available  the  eggs  are  deposited 
in  other  organic  material.  The  heat  generated  by  the  decom- 
position processes  which  occur  in  such  material  hatches  the 
larvae  or  maggots  from  the  eggs  in  one  day.  The  larvae  develop 
into  pupae  in  4  to  5  days  and  flies  emerge  3  to  4  days  later.  The 
time  from  the  egg  to  the  fly  is  8  to  10  days. 

It  is  recommended  that  manure  be  removed  to  the  fields  at 
intervals  of  seven  days  or  less  to  prevent  the  development  of 
the  flies,  but  this  plan  will  be  effective  only  when  the  manure  is 
stored  in  a  receptacle  which  has  a  tight  bottom,  because  the 
larvae  or  maggots  frequently  burrow  into  the  earth  to  pupate. 
The  larvae  also  bury  themselves  in  the  same  manner  in  an  earth 
stable  floor.  This  propensity  of  the  larvae  to  migrate  has  been 
made  use  of  to  trap  them  by  Hutchinson,  who  constructed  a 
trap  consisting  of  a  raised  platform  with  a  shallow  cement  tank 
beneath  it.  The  platform  is  made  of  wood  strips  1%  inches 
thick  and  1  inch  wide,  laid  1  inch  apart.  The  manure  is  piled 
compactly  on  the  platform,  each  day's  addition  being  moistened 
with  water.  When  the  larvae  are  hatched  they  migrate  down- 
ward and  fall  through  the  spaces  in  the  platform  into  the  water 
in  the  tank  below,  where  they  are  drowned. 

Numerous  experiments  have  been  made  to  discover  a  sub- 
stance which  when  mixed  with  horse  manure  would  destroy  the 
larvae  of  the  house-fly  without  affecting  the  fertilizing  value 
of  the  manure.  Naturally,  the  chemical  fertilizers  were  tested, 
but  it  was  found  that  acid  phosphate  and  ground  phosphate  rock 
will  not  kill  the  larvae,  while  kainit  (KC1  and  MgSO4)  possesses 
only  slight  larvaecidal  action.  In  several  experiments,  Cook  and 
Hutchinson  found  that  calcium  cyanamid  (CaCN2),  a  substance 
frequently  incorporated  in  commercial  fertilizers  to  furnish 
nitrogen,  apparently  destroyed  about  98  per  cent,  of  the  larvae 
when  applied  to  manure  at  the  rate  of  %  pound  to  the  bushel 
with  an  equal  quantity  of  acid  phosphate.  The  cost  of  this 
treatment  is  1.8  cents  per  bushel  of  manure,  but  the  fertilizing 
value  of  the  manure  is  considerably  in  creased,  «so  that  the  actual 
cost  is  much  less.  A  portion  of  the  acidi  phosphate  may  be  re- 
placed with  kainit  without  affecting  the  larvaecidal  effect  and  the 
mixture  will  then  contain  all  the  essential  elements  of  plant  food. 
Unfortunately,  calcium  cyanamid  can  be  purchased  only  in  car- 


164        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

load  lots  at  the  present  time,  but  if  a  demand  is  created  it  will 
no  doubt  be  available  in  smaller  quantities.  In  the  commercial 
fertilizers  it  is  usually  converted  into  urea,  ammonia,  etc.  Of 
the  various  substances  tested,  the  most  satisfactory  results  were 
obtained  with  powdered  hellebore  and  borax.  One-half  pound 
of  powdered  hellebore  is  mixed  with  10  gallons  of  water  and 
allowed  to  stand  24  hours.  This  quantity  is  sufficient  to  treat 
10  cubic  feet  (8  bushels)  of  manure,  being  applied  with  a 
sprinkler.  The  borax  is  applied  with  a  flour-sifter,  especially 
around  the  edges  of  the  manure  heap,  and  water  is  then  sprinkled 
over  it;  about  1  ounce  of  borax  and  2%  to  3  quarts  of  water 
are  used  to  each  cubic  foot  of  manure.  Floors,  crevices,  and  refuse 
may  be  treated  in  the  same  manner  with  either  hellebore  or  borax. 
Borax  is  perhaps  a  little  more  effective  as  a  larvaecide  than 
hellebore,  but  the  latter  is  not  at  all  injurious  to  the  manure  nor 
to  crops  while  borax  in  excessive  quantity  interferes  with  plant 
growth.  Manure  treated  with  borax  as  above  may  be  applied 
in  any  quantity  up  to  15  tons  per  acre  without  injuring  the 
crops,  except  in  the  case  of  leguminous  plants.  When  borax- 
treated  manure  is  used  to  grow  leguminous  plants,  it  should  be 
mixed  with  untreated  manure.  The  effect  of  the  repeated  appli- 
cation of  borax-treated  manure  has  not  been  determined.  The 
cost  of  treating  manure  with  powdered  hellebore  is  a  little  over 
%  cent  per  bushel,  while  the  expense  of  the  borax  treatment 
is  a  little  less  than  %  cent  per  bushel. 

The  cow-fly  or  horn-fly  lays  its  eggs  in  fresh  cow  manure. 
The  larvae  are  hatched  in  24  hours  and  develop  into  pupae  in  5 
days.  The  pupae  burrow  into  the  ground  and  flies  emerge  in  8 
days,  the  time  from  the  egg  to  the  fly  being  14  days. 

These  flies  feed  upon  the  blood  of  the  cow  and  are  therefore 
not  likely  to  get  into  the  milk  or  milk  vessels.  In  biting  through 
the  skin  of  the  cow  to  obtain  food,  they  cause  the  animal  con- 
siderable discomfort.  When  driven  off  the  body  of  the  cow,  they 
fly  only  a  short  distance  away  and  then  immediately  return,  so 
that,  while  feeding,  they  are  a  continual  torment. 

Fly  repellents  are  used  to  protect  the  cow  from  the  attacks 
of  these  insects.  A  mixture  of  one  part  of  oil  of  tar  and  nine 
parts  of  cotton-seed  oil  or  crude  Beaumont  oil,  applied  daily 


DAIRY  INSPECTION  165 

with  a  spray  pump  or  syringe,  is  an  effective  and  safe  repellent. 
The  following  mixture,  it  is  claimed,  will  act  effectively  for  one 
week:  Soap,  1  pound;  water,  4  gallons;  crude  petroleum,  1 
gallon,  and  powdered  naphthalene,  4  ounces.  The  soap  is  shaved 
into  thin  slices  and  dissolved  in  the  water  by  heating;  the 
naphthalene  is  dissolved  in  the  crude  oil.  The  two  solu- 
tions are  mixed  by  stirring  vigorously  or  churning  for  15 
minutes.  The  mixture  is  stirred  thoroughly  each  time  before 
using  and  is  applied  to  the  cows  with  a  brush  once  or  twice 
weekly.  While  fly  repellents  afford  the  cow  temporary  relief 
from  the  biting  flies,  they  are  of  no  value  in  the  control  or 
eradication  of  the  flies.  Hellebore  and  borax  have  not  been 
tested  on  the  larvae  of  the  cow-fly,  but  it  is  very  probable  that 
they  would  be  as  destructive  to  these  larvae  as  to  those  of  the 
house-fly. 

When  cows  are  kept  in  the  stable,  with  occasional  liberty 
in  an  exercise  yard,  the  breeding  of  cow-flies  can  be  prevented 
by  removing  the  manure  from  the  stable  and  yard  to  the  fields 
daily,  or  if  it  is  stored  in  the  vicinity  of  the  stable,  by  removing 
it  to  the  fields  at  intervals  of  not  less  than  12  days,  provided 
the  floor  of  the  stable  and  the  floor  of  the  dung-stead  are  so 
constructed  that  the  pupae  cannot  burrow  into  the  ground. 
When  cows  are  pastured  it  is  not  practicable  to  control  the 
breeding  of  cow-flies.  The  manure  dropped  in  the  pasture  fur- 
nishes ideal  breeding  conditions.  When  the  flies  emerge  they 
take  up  a  position  on  the  body  of  the  cow,  where  they  feed  and 
rest,  and  are  carried  into  the  stable  by  the  cow. 

The  stable-fly  breeds  in  horse  manure  and  in  decaying  grass 
and  straw  heaps ;  also  in  cow  droppings  which  have  become  dry 
and  disintegrated,  and  in  ensilage.  Eggs  deposited  in  these 
substances  hatch  out  larvae  in  1  to  3  days.  The  larvae  develop 
into  pupae  in  11  to  30  days  or  more,  and  the  flies  emerge  in 
6  to  20  days,  the  time  from  the  egg  to  the  fly  being  18  to  53 
days  and  upwards.  The  stable-fly  feeds  on  the  blood  of  cows 
and  other  domestic  animals,  and  also  bites  man.  Unlike  the 
house-fly,  it  is  not  likely  to  infect  milk  with  bacteria,  since  it 
does  not  feed  upon  that  substance. 


166        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

2.  Cleaning  the  Cows. — The  body  surface  of  the  cow 
may  be  soiled  with  dirt  and  manure  when  the  animal  lies 
down,  dust  settles  on  the  skin  from  the  air,  and  dead 
epidermal  cells  and  hair  are  cast  off  from  the  skin.  This 
material  is  very  rich  in  bacteria  and,  if  not  removed,  some 
of  it  will  be  dislodged  during  milking  and  may  fall  into 
the  milk  pail.  The  manure  contains  numerous  gas-form- 
ing and  putrefactive  bacteria  and  is  therefore  especially 
objectionable.  Dry  dirt  and  manure  should  be  loosened 
with  a  curry-comb  and  then  brushed  out  with  a  stiff  brush, 
which  will  also  remove  loose  hairs  and  epidermal  cells. 
If  the  dirt  or  manure  is  not  dry  it  must  be  washed  off  with 
a  clean  cloth  and  water.  The  addition  of  1  to  2  per  cent, 
of  washing  soda  (a  Mason  jar  lid  full  to  a  12  quart 
bucket)  is  of  great  assistance.  White  hair  is  likely  to 
show  a  stain  after  the  dirt  has  been  washed  off  and  this 
must  not  be  mistaken  for  dirt.  No  dust  can  be  rubbed 
out  of  an  area  that  is  only  stained.  In  cleaning  the  cows 
special  attention  should  be  given  to  the  udder,  flanks, 
external  surface  of  the  thighs  and  the  switch.  In  some 
dairies  the  switch  is  washed  at  short  intervals.  Keeping 
the  hair  clipped  short  on  these  parts  and  on  the  buttocks 
will  facilitate  the  work  of  cleaning.  It  is  advisable  to 
have  the  switch  clear  the  ground  by  about  4  inches,  but 
there  is  some  objection  to  cutting  the  switch  of  pure-bred 
cows. 

After  the  udder  has  been  brushed  dry  it  should  be 
wiped  with  a  damp  cloth.  The  cloth  and  water  should  be 
clean  at  the  start  and  the  water  should  be  changed  as 
soon  as  it  becomes  soiled.  Ordinarily,  a  bucket  of  clean 
water  is  required  for  every  eight  cows.  In  high-class 
dairies  a  small  damp  towel  is  used  for  each  cow;  each 
towel  is  used  only  once  and  is  then  washed  and  sterilized. 


DAIRY  INSPECTION  167 

The  brushing  should  be  finished  a  half  hour  before  milk- 
ing, to  allow  time  for  the  dust  to  settle  from  the  air  of 
the  stable,  but  the  udder  should  be  wiped  just  before 
milking  is  begun.  If  the  udder  is  brushed  immediately 
before  milking  the  number  of  bacteria  in  the  milk  will 
be  about  doubled.  The  practice  indulged  in  by  some 
milkers  of  attempting  to  clean  the  udder  by  wiping  it 
with  the  hand  after  sitting  down  to  milk  is  not  a  good 
one,  as  it  dislodges  a  lot  of  loose  hair,  epithelial  cells  and 
particles  of  dirt  which  may  fall  into  the  milk  pail.  The 
purpose  in  wiping  the  udder  with  a  damp  cloth  is  to 
moisten  any  loose  dirt,  hair,  etc.,  that  may  remain  after 
brushing  and  thus  prevent  these  particles  from  falling 
into  the  milk. 

The  number  of  bacteria  dislodged  from  apparently 
clean  udders  by  the  process  of  milking  is  reduced  about 
two-thirds  by  dampening  the  surface  of  the  udder.  Too 
much  water  should  not  be  used,  as  any  excess  will  run 
off  the  end  of  the  teat  and  may  drop  into  the  milk  pail, 
while,  in  winter,  the  exposure  of  a  wet  udder  to  cold  air 
is  very  likely  to  cause  congestion  and  cracking  of  the 
skin,  especially  at  the  base  of  the  teats  and  on  the  teats, 
and  may  also  cause  catarrhal  mastitis.  Washing  the 
udder,  unless  it  is  afterward  rubbed  dry,  is  not  as  effective 
in  keeping  dirt  and  bacteria  out  of  milk  as  is  wiping  it 
with  a  damp  cloth  after  dry  brushing.  The  best  results 
are  obtained  by  wiping  the  udder  with  a  cloth  dampened 
with  a  2  per  cent,  solution  of  washing  soda  after  it  has 
been  cleaned  by  brushing,  and  then  anointing  it  with  a 
small  quantity  of  vaseline.  As  much  vaseline  as  can  be 
taken  up  on  the  end  of  the  finger  is  rubbed  over  the 
palms  of  the  hands,  which  are  then  passed  lightly  over 
the  udder.  This  method  takes  less  time  than  washing 


168         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

the  udder,  while  the  skin  covering  the  teats  remains  soft 
and  pliable  and  there  is  an  entire  absence  of  cracks  and 
sores,  even  in  winter. 

It  is  sometimes  stated  that  dampening  or  washing  the 
udder  irritates  the  skin,  causing  it  to  swell  and  crack,  and 
that  it  decreases  the  milk  flow,  but  this  is  not  entirely 
correct.  The  udder  will  suffer  no  injury  whatever  unless 
too  much  water  is  used  and  the  organ  is  exposed  to  cold 
air  in  a  wet  condition.  There  may  be  a  decrease  in  the 
milk  secretion  when  a  cow  is  subjected  to  the  process 
for  the  first  time,  but  the  milk  flow  returns  to  normal  in 
a  few  days  and  very  frequently  it  is  increased.  The  mas- 
sage which  accompanies  the  brushing  and  the  wiping  or 
washing  favors  the  flow  of  blood  to  the  udder  and  usually 
increases  the  secretion  of  milk.  Udders  which  are  kept 
clean  are  affected  with  disease  less  frequently  than  dirty 
udders. 

As  a  general  rule,  cows  will  produce  more  milk  when 
kept  clean  and  comfortable  than  when  they  are  kept 
otherwise.  Therefore  cleaning  the  cows  not  only  assists 
in  keeping  dirt  and  bacteria  out  of  the  milk  but  usually 
also  increases  the  milk  production.  After  the  cows  have 
been  cleaned  they  should  be  fastened  so  that  they  cannot 
lie  down  before  they  are  milked. 

3.  Methods  of  Milking. — The  condition  of  the  milker 
as  regards  health  and  cleanliness  should  receive  the  atten- 
tion of  the  inspector.  No  one  should  be  permitted  to 
milk  cows  or  handle  milk  in  any  way  who  is  affected  with 
any  infectious  disease,  especially  typhoid  fever,  diph- 
theria, and  scarlet  fever,  or  who  has  been  in  contact  with 
persons  affected  with  any  of  these  diseases.  Persons 
affected  with  tuberculosis,  syphilis,  severe  diarrhoea, 
suppurating  sores  on  exposed  surfaces,  or  any  throat 


DAIRY  INSPECTION  169 

disease  should  also  be  debarred  from  employment  on  a 
dairy  farm. 

The  milker  should  have  special  clothing  to  wear  while 
milking.  Considerable  dust  and  dirt  collects  on  the  outer 
surface  of  clothing  worn  while  cleaning  the  cows  and 
stable  or  in  doing  farm  work,  especially  if  it  is  made  of 
material  with  a  soft,  rough  finish,  and  a  good  deal  of  this 
dirt  may  drop  off  into  the  milk  pail  during  milking.  A 
clean  blouse,  overalls,  and  a  cap  should  therefore  be  put 
on  before  beginning  to  milk.  These  should  be  made  of 
washable  material  with  a  smooth,  hard,  finish  like  duck, 
linen,  or  drilling.  White  linen  or  duck  is  best.  One  or 
two  suits  a  week  in  winter  and  two  or  three  in  summer 
will  be  required  in  order  to  have  a  reasonably  clean  suit 
at  all  times.  An  apron  or  a  pair  of  overalls  with  a  bib 
is  sometimes  used  because  they  are  easier  to  put  on  and 
off;  but  they  do  not  cover  the  shoulders  and  arms,  the 
parts  from  which  dirt  is  most  likely  to  be  dislodged  in 
milking. 

Before  beginning  to  milk,  the  milker  should  wash  his 
hands  thoroughly,  using  soap,  water  and  a  nail  brush,  and 
dry  them  carefully  with  a  clean  towel.  After  doing  so, 
he  should  not  touch  anything  but  the  teats  of  the  cow, 
milk  pail,  and  milk  stool.  The  inspector  should  note 
what  facilities  are  provided  for  washing  and  drying  the 
hands. 

When  the  milking  of  a  cow  is  finished,  the  pail  should 
be  carried  to  the  weigh  room  and  the  milk  weighed  and 
emptied,  the  weight  of  the  milk  being  recorded  on  the 
milk  record  opposite  the  name  or  number  of  the  cow.  In 
passing  in  the  rear  of  the  cows,  the  milk  pail  should  be 
carried  on  the  side  of  the  body  furthest  away  from  the 
cows ;  covered-top  pails  should  be  carried  with  the  open- 


170        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

ing  on  the  opposite  side  from  the  body.  This  will  protect 
the  milk  from  contamination  by  cows  switching  the  tail, 
splashing  of  manure  or  urine,  and  dirt  falling  from  the 
clothing  of  the  milker.  The  milker  should  wash  his  hands 
again  before  milking  another  cow  and  should  dry  them 
well  on  a  clean  towel.  Small,  individual  towels,  about 
10  x  10  inches,  which  can  be  used  once  and  then  thrown 
aside  for  washing,  are  much  more  desirable  than  a  large 
towel  used  in  common  by  several  milkers. 

Soiled  hands  are  a  prolific  source  of  bacteria  in  milk. 
As  many  as  45,000,000  bacteria  have  been  found  on  one 
hand  of  a  farm  laborer.  Washing  and  drying  the  hands 
will  reduce  the  number  of  bacteria  75  per  cent,  or  more, 
and  also  decrease  the  danger  from  chronic  typhoid  bacilli 
carriers.  Experiments  indicate  that  careful  drying  is 
quite  as  important  as  thorough  washing,  fewer  organisms 
remaining  after  careful  drying  than  when  the  hands  are 
rinsed  in  an  antiseptic  solution  after  washing  and  are  not 
carefully  dried. 

Milking  should  be  done  with  dry  hands.  When  the 
hands  are  wet  the  moisture  assists  in  loosening  the  epi- 
dermal cells  and  dirt  from  the  surface  of  the  teat,  and  this 
material  gradually  moves  down  to  the  end  of  the  teat 
and  drops  off  into  the  milk  pail.  The  practice  of  wetting 
the  hands  with  milk  when  beginning  to  milk  is  to  be  con- 
demned because  this  milk,  after  being  mixed  with  the 
dirt  on  the  teats,  drops  off  into  the  pail. 

Sometimes  dairymen  claim  that  it  is  sufficient  to  wash 
the  hands  before  beginning  to  milk,  saying  that  if  the 
udders  are  clean  the  hands  will  not  become  soiled.  This 
would  be  true  if  the  udders  were  bacteriologically  clean 
and  if  the  milker  did  not  touch  anything  but  the  clean 
teats  of  the  udder.  But  the  milker  sometimes  touches 


DAIRY  INSPECTION  171 

other  parts  of  the  cow  in  pushing  or  striking  the  animal 
to  cause  it  to  stand  over  in  the  stall  and  in  protecting 
himself  against  a  switching  tail.  In  addition,  the  milk 
bucket  is  often  rested  on  the  floor  and  the  bottom  subse- 
quently grasped  in  emptying  it,  thus  soiling  the  fingers 
with  material  from  the  floor.  The  milking  stool  may  be 
another  source  of  contamination  for  the  hands.  It  should 


FIG.  13. — Open  or  uncovered  pail.  FIG.  14. — Covered-top  pail  with  opening 

nearly  horizontal  (with  strainer  attached). 

therefore  be  kept  clean  and  it  is  best  to  use  one  made  of 
metal. 

The  milk  should  be  drawn  without  jerking  the  teats, 
as  this  dislodges  dirt  and  bacteria  which  are  liable  to  fall 
into  the  milk.  "  Stripping  "  the  teats  is  also  objection- 
able for  the  same  reason.  The  first  few  streams  of  milk 
(fore-milk)  from  each  quarter  should  be  drawn  into  a 
separate  vessel,  as  this  milk  washes  out  the  milk  cistern 
and  teat  canal  and  contains  a  greater  number  of  bacteria 
than  the  milk  subsequently  drawn  from  the  udder.  The 


172        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

fore-milk  from  a  normal  udder  usually  contains  from 
0  to  500  bacteria  per  c.c.,  mostly  udder  cocci.  Sometimes 
more  may  be  present,  but  when  the  number  exceeds 
5000  per  c.c.  the  udder  is  infested  with  mastitis  organ- 
isms, usually  streptococci.  The  fore-milk  should  not  be 
milked  out  upon  the  floor  or  litter  as  this  supplies  condi- 
tions which  are  favorable  to  the  growth  of  bacteria. 

The  type  of  milk  pail  has  a 
very  pronounced  influence  on  the 
bacterial  content  of  milk.  The 
larger  and  more  horizontal  the 
opening  of  the  pail  the  greater  the 
opportunity  for  contamination. 
There  are  two  types :  The  open  or 
uncovered  pail  and  the  covered-top 
pail  (Figs.  13,  14,  and  15).  The 
top  of  the  open  pail  is  entirely  un- 
protected and  is  about  12  inches  in 
diameter,  while  the  covered-top 
pail  has  an  opening  only  7  inches 
in  diameter,  the  remainder  of  the 
top  being  covered.  The  smaller 
opening,  of  course,  offers  much  less 
opportunity  for  dirt  to  fall  into  the  FlQ 
milk.  It  is  more  difficult  to  milk  vertical  opening- 

into  the  covered-top  pail  than  into  the  open  pail,  especi- 
ally at  first,  but  this  is  largely  overcome  by  practice. 
There  are  two  varieties  of  covered-top  pails :  One  with 
the  opening  vertical  and  protected  by  a  hood  and  the 
other  with  the  opening  more  or  less  horizontal  (Figs. 
14  and  15) .  The  pail  with  the  vertical  opening  is  prob- 
ably somewhat  more  difficult  to  milk  into  than  the  pail 
with  the  horizontal  opening,  but  it  affords  a  much  greater 


DAIRY  INSPECTION 


173 


protection  against  the  contamination  of  the  milk  than  the 
pail  with  the  horizontal  opening,  even  when  the  latter 
contains  a  cheese-cloth  and  wire-gauze  strainer.  Some 
varieties  of  pails  in  which  strainers  are  used  have  a  spout 
on  the  side  so  that  they  can  be  emptied  without  removing 
the  strainer.  There  is  one  type  of  pail  which  has  no 
opening  in  the  top,  but  a  spout  extending  from  the  side 


FIG.  16. — Another  variety  of  covered-top  pail.     The  milker  sits  on  the  pail  and  milks  into 
the  funnel,  which  is  covered  with  a  cheese-cloth  strainer. 

has  a  funnel  in  the  end  to  receive  the  milk.  The  milker 
sits  on  the  pail  and  milks  into  the  funnel.  When  the  pail 
is  to  be  emptied  the  funnel  is  removed  and  the  milk  is 
poured  out  of  the  spout.  Pails  with  several  parts  are 
not  as  easily  kept  clean  as  the  other  kind.  Every  addi- 
tional piece  of  apparatus  not  only  increases  the  work  of 
cleaning  but  also  provides  another  possible  medium  for 
the  conveyance  of  bacteria  to  milk. 

Strainers  of  cheese  cloth  and  wire  gauze  cannot  be 


174        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

depended  upon  to  protect  milk  from  contamination. 
They  do  not  keep  out  bacteria,  but  hold  back  only  the 
larger  particles  of  dirt.  Some  of  these  particles  are  sub- 
sequently dissolved  by  milk  and  carried  through  the 
strainer,  while  bacteria  are  washed  off  of  the  insoluble 
particles  remaining  on  the  strainer.  It  is  also  difficult 
to  clean  strainers  of  this  kind  thoroughly.  Particles  of 
dirt  become  entangled  in  the  meshes  of  the  wire  gauze, 
especially  at  the  periphery  where  it  is  soldered  to  the  tin, 
and  it  is  difficult  to  remove  them,  while  the  cheese  cloth 
requires  much  care  in  cleaning.  It  should  be  rinsed  in 
cold  water,  washed  in  hot  water  containing  two  per  cent, 
of  soda,  again  rinsed  in  cold  water  and  then  wrapped  in 
a  clean  cloth  and  sterilized  in  a  steam  chest.  If  a  steam 
chest  is  not  available,  it  should  be  put  into  a  thick  paper 
sack  and  placed  in  a  stove  oven  and  kept  there  until  the 
sack  begins  to  scorch.  A  strainer  composed  of  a  thin 
layer  of  absorbent  cotton  is  much  more  effective  and  it 
can  be  thrown  away  after  being  used  and  thus  save  the 
labor  of  cleaning.  Some  of  the  bacteria  are  apparently 
enmeshed  in  the  cotton  and  kept  out  of  the  milk.  The 
use  of  a  cotton  strainer  has  reduced  the  bacterial  content 
of  the  milk  nearly  one-third  in  some  tests.  Coarse  cot- 
ton-flannel and  turkish  toweling  are  also  used  for  strain- 
ers, but  they  are  no  more  effective  than  cheese  cloth. 

Bacteria  cannot  be  kept  out  of  milk  by  strainers  nor 
can  they  be  removed  by  these  contrivances  after  they 
have  entered  the  milk.  The  coarse  particles  of  dirt  may 
be  strained  out,  but  the  most  objectionable  part  of  the 
dirt  the  bacteria,  will  remain.  Much  more  satisfactory 
results  will  be  obtained  by  cleanliness  and  care  in  milking 
and  in  the  subsequent  handling  of  the  milk. 

In  some  receiving  stations  and  distributing  plants, 


DAIRY  INSPECTION  175 

milk  is  run  through  a  machine  known  as  a  clarifier,  in 
which  the  milk  is  centrifugalized  and  the  heavier  sub- 
stances, such  as  dirt  particles,  cells,  and  some  of  the  bac- 
teria, separated  from  it.  The  process  is  known  as  clari- 
fication. When  determined  by  the  plate  method,  the 
number  of  bacteria  is  frequently  greater  after  clarifica- 
tion than  before,  but  this  increase  is  probably  due  to  the 
breaking  up  of  clumps  of  organisms  by  the  centrif  ugali- 
zation.  Some  of  the  bacteria  are  removed  from  the  milk 
since  the  sludge  or  residue  remaining  in  the  clarifier 
contains  bacteria  in  considerable  numbers.  The  per- 
centage removed  cannot  be  very  great,  however,  because 
the  milk  is  exposed  to  the  separating  action  for  only  a 
short  time.  The  sludge  or  residue  is  composed  very 
largely  of  the  amorphous  substances  normally  present  in 
milk,  the  remainder  consisting  of  bacteria,  cells,  hair,  and 
particles  of  dirt.  If  clarified  milk  is  subsequently  centri- 
fugalized for  three  minutes  at  3000  revolutions  per  min- 
ute, sediment  will  be  deposited,  showing  that  all  of  the 
sediment  is  not  removed  by  clarification.  All  gross  sus- 
pended dirt,  such  as  hairs,  dust  particles,  etc.,  are,  how- 
ever, removed  by  the  clarifier,  and  for  this  purpose  it  has 
many  advantages  over  strainers.  But  milk  containing 
pathogenic  organisms  is  no  cleaner  from  a  hygienic 
standpoint  after  clarification  than  before  (Bahlman, 
Hammer). 

4.  Feeding. — The  cows  should  not  be  fed  immedi- 
ately before  milking.  When  hay  or  other  dry  fodder 
is  brought  into  the  stable  and  distributed  around  among 
the  cows,  more  or  less  dust  is  liberated.  This  dust  con- 
tains numbers  of  bacteria,  principally  peptonizers,  and 
if  milking  is  done  while  it  is  floating  about  in  the  stable 
air  some  of  these  organisms  will  get  into  the  milk.  If 


176        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

the  hay  or  fodder  is  thrown  down  directly  into  the  stable 
from  a  loft  above,  the  quantity  of  dust  set  free  in  the 
stable  air  is  much  greater  than  when  it  is  thrown  down 
into  a  passageway  outside  of  the  stable.  Feeding  meal 
or  ground  grain  immediately  before  milking  is  also  objec- 
tionable, and  for  the  same  reason.  It  is  not  necessary  to 
feed  cows  before  milking  to  keep  them  quiet  during  milk- 
ing; they  soon  become  accustomed  to  being  fed  after 
milking. 

The  investigations  of  Ruehle  and  Kulp1  indicate  that 
under  ordinary  conditions  dust  in  the  stable  air  is  not 
nearly  as  much  concerned  in  the  bacterial  contamination 
of  milk  as  has  been  generally  believed,  but  as  it  is  only 
necessary  to  perform  the  several  stable  operations  in  a 
certain  order,  and  does  not  require  additional  labor,  to 
protect  milk  against  this  source  of  contamination  it  is 
advisable  to  take  this  precaution,  especially  since  un- 
usual conditions  which  will  increase  the  infection  from 
this  source  are  likely  to  prevail  at  times. 

The  feeding  of  ensilage  fills  the  air  of  the  stable  for 
a  time  with  the  odor  characteristic  of  this  substance,  and 
if  milking  is  done  during  this  period  the  odor  and  taste 
of  the  milk  is  likely  to  be  tainted.  This  is  likewise  true  of 
cabbage  and  rape,  and  also  of  beets,  turnips,  rutabagas 
and  carrots,  and  their  tops  (see  page  29) .  Odors  in  the 
stable  are  very  quickly  absorbed  by  milk,  especially  when 
it  is  warm. 

Sudden  changes  of  feed  and  overfeeding  should  be 
avoided.  A  sudden  change  from  dry  to  green  feed  will 
produce  diarrhoea.  Old  and  highly  acid  ensilage  and 
sometimes  overfeeding  will  have  the  same  effect.  Indi- 

1  Geneva,  N.  Y.,  Expt.  Sta.  Bull.  No.  409. 


DAIRY  INSPECTION  177 

vidual  milk  from  cows  in  this  condition  contains  prop- 
erties which  cause  digestive  and  intestinal  disturbances 
in  infants ;  when  sufficiently  diluted  with  milk  from  cows 
in  normal  condition,  it  is  not  likely  to  have  this  effect. 
The  presence  of  diarrhoea  also  increases  the  difficulty  of 
producing  clean  milk.  No  grain,  meal,  or  fodder  that 
is  musty,  mouldy,  or  otherwise  unsound  should  be  fed 
to  milch  cows.  Diarrhoea  has  been  observed  in  persons 
ingesting  milk  from  cows  receiving  feed  of  this  kind.  It 
has  been  assumed  that  the  diarrhoea  was  due  to  substances 
formed  in  the  feed  being  excreted  in  the  milk,  but  it  is 
possible  that  in  such  cases  the  fungi  or  bacteria  responsi- 
ble for  the  change  in  the  feed  pass  directly  from  the  feed 
to  the  milk  after  it  is  drawn  from  the  udder  and  bring 
about  decomposition  changes.  The  use  of  distillery  waste 
or  slop  and  of  wet  brewers'  grains  is  prohibited  by  law 
in  some  sections.  These  substances  when  fed  fresh  in 
moderate  quantity  have  no  injurious  effect  upon  the 
milk,  but  when  they  are  fed  in  an  advanced  stage  of 
fermentation  or  putrefaction  the  milk  may  cause  diges- 
tive disturbances,  especially  in  babies,  and  the  manure 
of  the  cows  has  a  bad  odor  and  is  very  soft.  In  addi- 
tion, when  these  substances  are  fed  it  is  difficult  to  keep 
the  stable  clean  and  free  from  bad  odors,  especially  the 
mangers  and  storage  bins  or  pits.  Particles  of  the  feed 
remain  in  corners  and  crevices  and  decompose,  produc- 
ing a  foul  odor.  On  the  other  hand,  dried  distillers'  grains 
and  dried  brewers'  grains  are  entirely  wholesome  feeds. 
It  is  advisable  to  water  the  cows  at  least  twice  daily. 
Whether  the  water  is  given  before  or  after  feeding  is 
of  no  consequence,  but  it  is  important  that  a  sufficient 
quantity  be  given.  The  greater  the  milk  production, 
the  more  water  required. 

12 


178        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

5.  Bedding. — Bedding  or  litter  assists  in  keeping 
the  cow  clean  and  affords  some  protection  against  a  hard, 
cold  floor;  it  also  assists  in  keeping  floors  clean  and  dry, 
especially  those  of  wood  and  earth,  by  absorbing  the 
liquid  manure.  Actual  test  has  shown  that  when  beef 
cattle  are  well-bedded  they  lie  down  more  frequently 
and  for  longer  periods  and  make  a  greater  gain  in  weight 
in  proportion  to  the  feed  consumed  than  they  do  under 
less  comfortable  conditions,  and  it  is  reasonable  to  assume 
that  dairy  cows  are  affected  in  a  similar  manner. 

The  materials  usually  used  for  bedding  are  wheat 
straw,  shredded  corn  fodder,  shavings,  and  sawdust. 
From  a  hygienic  standpoint,  shavings  and  sawdust  are 
the  most  satisfactory.  They  keep  the  cows  cleaner  and 
are  less  dusty  than  shredded  corn  fodder  or  straw,  but 
they  decay  more  slowly  and  are  not  as  satisfactory  in 
supplying  humus  to  the  soil.  Shredded  corn  fodder  and 
straw  are  about  equally  dusty,  but  the  cows  can  be  kept 
cleaner  with  the  former.  Cut  straw  is  less  satisfactory 
than  uncut.  Shredded  corn  fodder  excells  all  of  the 
others  in  absorbing  liquids,  with  shavings  next  in  order, 
then  straw,  and  finally  sawdust.  The  low  absorption 
power  of  sawdust  is  due  to  the  fact  that  it  is  usually 
damp  from  exposure  to  rain.  Sawdust  is  the  cheapest 
material  for  bedding  in  localities  where  it  is  available. 
Where  there  is  a  convenient  market  for  corn  fodder 
and  straw,  or  where  the  fodder  can  be  used  for  feed,  it 
will  pay  to  buy  shavings  for  bedding. 

All  bedding  material,  except  sawdust  when  it  is 
damp,  being  more  or  less  dusty,  should  be  put  down 
in  the  stable  after  the  milking  has  been  completed.  This 
is  especially  necessary  when  corn  fodder  or  straw  is  used, 
as  the  dust  in  these  is  likely  to  contain  large  numbers 


DAIRY  INSPECTION  179 

of  peptonizing  bacteria.  Mouldy  or  musty  straw  is  ob- 
jectionable because  it  contains  bacteria  and  fungi  which 
affect  the  keeping  qualities  and  wholesomeness  of  the 
milk. 

The  time  required  to  perform  the  various  stable  prac- 
tices described  in  the  preceding  pages  is  of  importance 
to  the  milk  producer,  and  the  inspector  should  there- 
fore be  familiar  with  this  side  of  the  subject.  The  fol- 
lowing figures  were  obtained  from  the  manager  of  a 
large  and  successful  dairy  farm  and  represent  the  aver- 
age time  required  by  different  men  to  perform  each 
operation,  the  men  being  timed  without  their  knowl- 
edge :  Taking  up  manure,  %  minute  for  each  cow  4  times 
daily. 

Sweeping  platforms,  stable  floor,  and  feed  troughs, 
and  wiping  stanchions,  1%  minutes  for  each  cow  twice 
daily. 

Grooming,  2%  minutes  for  each  cow  twice  daily. 

Washing  flanks  and  tails,  %  minute  for  each  cow 
twice  daily. 

Washing  udders,  two  waters,  %  minute  for  each  cow 
twice  daily. 

Drying  udders  and  drawing  fore-milk,  %  minute 
for  each  cow  twice  daily. 

Bedding,  %  minute  for  each  cow  twice  daily. 

Feeding,  1%  minutes  each  cow  twice  daily. 

Total  time  per  cow,  about  8%  minutes  twice  daily. 

IV.    MILK  HOUSE 

On  every  farm  where  milk  is  produced  there  should 
be  a  special  room  or  compartment  to  which  the  milk 
can  be  removed  immediately  after  it  is  drawn  from  the 
cow  and  where  it  can  be  subjected  to  some  method  of 


180        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

cooling.  When  the  milk  from  the  individual  cows  is 
emptied  into  a  shipping  can  in  the  stable,  it  is  exposed 
to  contamination  by  any  dust  or  odors  which  may  be 
present  in  the  stable  air,  and,  furthermore,  it  is  not  likely 
to  be  promptly  cooled.  A  milk  room  is  therefore  a  neces- 
sity. On  dairy  farms  it  has  been  found  to  be  convenient 
as  well  as  economical  to  have  this  room  in  the  same  build- 
ing with  other  rooms  in  which  the  utensils  and  vessels 
can  be  washed  and  in  which  the  milk  can  be  stored.  A 
building  of  this  kind  is  called  a  milk  house  or  dairy  build- 
ing and  sometimes  also  contains  a  room  in  which  the 
milk  is  bottled.  A  spring  house  may,  when  the  condi- 
tions are  suitable,  serve  as  a  substitute  for  a  storage  room 
or  refrigerator,  but  the  practice  of  washing  the  milk  ves- 
sels in  the  kitchen  of  the  dairyman's  residence  is  very 
objectionable.  The  milk  house  should  be  arranged  so 
that  it  will  not  be  necessary  for  the  milkers  to  enter  the 
room  in  which  the  cooler  is  located  or  to  pass  through 
the  wash  room  to  empty  their  milk  pails.  This  will 
greatly  reduce  the  labor  of  keeping  the  several  rooms 
clean.  The  floor  plan  of  a  milk  house  in  which  this  idea 
is  carried  out  is  shown  in  Fig.  17.  The  milkers  pass 
from  the  stable  to  the  weigh  room,  where  the  milk,  after 
being  weighed,  is  emptied  into  a  tank,  from  which  it 
is  carried  by  a  short  pipe  passing  through  the  wall  to  the 
reservoir  on  top  of  the  milk  cooler. 

The  inspector  should  observe  the  location  of  the  milk 
room  or  milk  house  and  the  materials  of  which  it  is  con- 
structed; note  the  provisions  for  cooling  the  milk;  exam- 
ine the  condition  of  the  apparatus  and  utensils  and  the 
facilities  for  washing  and  cleaning  them,  and  investigate 
the  source  of  the  water  used  for  the  latter  purpose. 

1 .  Location. — The  milk  house  should  be  isolated  from 


DAIRY  INSPECTION 


181 


driveways,  in  so  far  as  this  is  possible,  and  there  should 
be  an  open-air  space  between  it  and  the  stable.  If  the 
milk  room  is  not  entirely  separated  from  the  stable,  the 
chief  object  of  having  it,  namely,  to  protect  the  milk 
from  the  stable  air,  will  be  defeated.  If  the  surrounding 
grounds  are  dusty  or  if  much-used  dirt  roads  are  close 
to  it,  the  atmosphere  in  the  building  will  be  dusty.  Some 


. — Floor  plan  of  a  conveniently  arranged  milk  house.  A,  receiving  funnel;  B, 
milk  cooler;  C,  bottle  filler;  D,  refrigerator;  E,  cooling  tank;  F,  sterilizer;  G,  Babcock 
tester;  H,  bottle  washer;  I,  concrete  sink;  J,  boiler;  K,  chimney;  L,  floor  drains;  M, 
sunning  rack;  N,  separator.  (Hoard's  Dairyman). 

system  of  drainage  is  necessary  to  carry  off  waste  water 
and  washings,  otherwise  the  air  may  become  foul  from 
decomposing  milk. 

2.  Construction. — On  entering  the  milk  house,  the 
inspector  should  first  note  the  odor  of  the  air.  A  sour 
or  putrid  odor  indicates  uncleanliness  or  defective  drains. 
A  musty  or  mouldy  odor  results  from  lack  of  ventilation. 
The  floor,  walls,  and  ceiling  should  be  examined,  the 
material  of  which  they  are  constructed  and  their  condi- 


182         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

tion  in  regard  to  cleanliness  being  noted.  Cement  is  the 
best  material  because  it  can  be  most  readily  cleaned,  but 
smooth  boards  with  tight  joints,  oiled  or  painted,  will 
do  fairly  well  for  the  walls  and  ceiling,  although  it  is 
desirable  to  have  the  walls  finished  in  cement  for  about 
four  feet  above  the  floor,  especially  in  the  room  used 
for  washing  the  milk  vessels  and  utensils.  The  floor 
should  always  be  constructed  of  cement.  The  lighting 
should  also  be  observed.  There  should  be  a  sufficient 
number  of  windows  to  furnish  good  light,  and  some  good 
method  of  artificial  lighting  is  also  desirable.  All  win- 
dows and  doors  should  be  screened  against  flies. 

3.  Apparatus. — The  apparatus  present  in  the  milk 
house  and  its  condition  should  be  observed.  There  ought 
to  be  some  means  of  cooling  the  milk  and  keeping  it 
cool,  and  there  should  be  facilities  for  cleaning  the  milk 
vessels  and  utensils,  including  a  convenient  and  plenti- 
ful supply  of  hot  and  cold  water.  If  the  milk  is  bottled, 
a  bottle  washer,  bottle  filler,  and  bottle  capper  should 
be  provided.  These  need  not  necessarily  be  expensive. 
A  sterilizer  is  also  desirable.  It  is  a  protection  against 
the  contamination  of  the  milk  through  returned  bottles 
and  it  is  also  a  great  aid  in  keeping  the  milk  vessels  and 
utensils  clean.  A  bottle  filler  and  capper  will  guard 
the  milk  against  contamination  by  the  fingers. 

A  cooler,  sometimes  called  an  aerator,  is  necessary 
for  the  rapid  cooling  of  milk.  This  apparatus  is  con- 
structed so  that  the  milk  flows  in  a  thin  layer  over  a 
sheet  of  tinned  metal  while  cold  water  or  brine  flows 
on  the  other  side  of  the  metallic  sheet  and  absorbs  heat 
from  the  milk.  There  are  four  types  of  milk  coolers: 
(a)  conical,  (  b)  corrugated,  (c)  tubular,  and  (d)  inter- 
nal or  double-tube. 


DAIRY  INSPECTION  183 

(a)  The  conical  cooler  (Fig.  18)  is  a  cone-shaped 
tank  with  a  gutter  around  the  base  and  a  movable  reser- 
voir at  the  top.  The  reservoir  has  small  perforations 
in  the  bottom  around  the  periphery.  When  the  cooler 
is  in  use,  the  cavity  of  the  tank  is  filled  with  water  or 
ice  water.  The  milk  is  poured  into  the  reservoir  and, 
passing  out  through  the  perforations,  flows  in  a  thin  layer 
down  over  the  external  surface  of  the  conical  tank,  col- 
lecting in  the  gutter  at  the  bottom.  From  the  gutter 
it  is  permitted  to  run  into  the  shipping  can  or  bottler. 


PERFORATIONS-  -- 


COOLING  DRUM 


TROUGH  TO 
COLLECT  MtLK, 


Fia.  18.—  Cooler  of  conical  type. 


One  model  of  this  type  of  cooler  has  attachments 
for  pipe  or  hose  to  carry  cold  water  into  the  tank  and 
to  remove  the  water  which  has  been  warmed  by  the  heat 
absorbed  from  the  milk;  another  which  is  intended  for 
use  on  farms  without  a  water  pipe  system  does  not  have 
these  attachments,  and  the  warm  water  must  be  removed 
and  the  cold  water  added  with  a  dipper  or  similar  vessel. 

(  b  )  The  corrugated  type  (  Fig.  19  )  of  cooler  consists 
of  two  sheets  of  corrugated  copper,  with  a  small  water- 
tight space  between  them  and  tinned  on  the  outer  sur- 
face. The  cooling  fluid  enters  through  a  pipe  at  the 


184        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

lower  part  of  this  space  and  discharges  at  the  top.  The 
milk  is  poured  into  a  reservoir  or  tank  at  the  top  of 
the  corrugated  metallic  sheets  and,  passing  out  through 
perforations  in  the  bottom  of  the  reservoir,  flows  slowly 
downward  in  a  thin  layer  over  the  corrugated  surfaces 
to  a  trough  at  the  bottom,  from  which  it  passes  into  the 


Fio.  19. — Corrugated  type  of  cooler. 

collecting  can  or  bottling  apparatus.  A  late  model  of 
the  corrugated  type  of  cooler  is  conical  in  form  and  is 
provided  with  a  metal  cover  to  protect  the  milk  from 
contamination  while  it  is  passing  over  the  cooling  sur- 
face. 

(c)   The  tubular  cooler  (Fig.  20)  consists  of  a  num- 
ber of  pipes  arranged  horizontally,  one  under  the  other 


DAIRY  INSPECTION 


185 


and  close  together.  They  are  connected  at  either  end 
so  that  fluid  can  flow  from  one  tube  into  another.  The 
cooling  fluid  enters  the  bottom  pipe  and  flows  upward 
through  the  various  pipes,  while  the  milk  flows  down- 
ward over  the  outer  surface  of  the  pipes  from  a  reservoir 


Fio.  20. — Tubular  cooler,  with  continuous  surface. 

at  the  top  and  is  received  in  a  collecting  tank  at  the 
bottom.  In  some  coolers  of  this  type  the  pipes  can  be 
taken  out  to  be  cleaned  and  sterilized.  Sometimes  these 
coolers  are  arranged  for  ice  water  to  run  through  the 
lower  pipes  and  water  through  the  upper  pipes,  the 
object  being  to  save  ice.  The  corrugated  coolers  have 
an  ice-water  section  which  can  be  attached  to  the  bottom. 


186        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

(d)  The  internal  or  double-tube  cooler  (Fig.  21) 
is  a  system  of  double  pipes,  one  within  the  other.  The 
milk  flows  through  the  inner  pipes  and  the  cooling  fluid 
through  the  outer.  In  this  type  of  cooler  the  milk  is 
protected  from  possible  contamination  from  the  air.  To 
facilitate  cleaning,  the  connections  between  the  individual 
pipes  are  removable  (detachable  return  bends). 

With  a  cooler,  the  temperature  of  milk  can  be  low- 
ered to  within  a  few  degrees  of  the  cooling  fluid  in  a 
few  minutes,  provided  the  apparatus  is  not  pushed  be- 
yond its  capacity.  If  the  cooler  is  not  large  enough, 
the  milk  is  likely  to  be  permitted  to  flow  over  the  cooling 
surface  too  rapidly  for  much  of  the  heat  to  be  absorbed 
by  the  cooling  fluid.  The  size  of  the  cooler  required 
will  depend  on  the  quantity  of  milk  to  be  cooled  and 
the  number  of  milkers.  The  capacity  of  coolers  as  stated 
by  manufacturers  is  usually  based  on  20  square  feet  of 
cooling  surface  per  1000  pounds  of  milk. 

Milk  should  be  cooled  to  as  low  a  temperature  as 
possible,  and  should  be  kept  cool.  The  lower  the  tem- 
perature, the  slower  the  bacterial  growth  and  the  longer 
the  milk  will  keep  in  good  condition  (see  page  43). 
Above  60°  F.  the  bacteria  multiply  rapidly,  and  at  70° 
F.  or  above  growth  is  not  only  very  rapid,  but  the  de- 
velopment of  the  more  objectionable  bacteria  is  favored. 
When  well  water  or  spring  water  is  used  for  the  cooling 
fluid,  the  temperature  of  the  milk  cannot  be  reduced 
much  below  60°  F.  and  often  not  that  low.  The  tem- 
perature of  well  and  spring  water  in  the  section  around 
Philadelphia  ranges  from  52  to  55°  F.  in  the  spring 
and  summer  months,  but  in  the  late  summer  and  early 
fall  it  is  usually  higher,  especially  in  sandy  regions,  rising 
to  69  and  70°  F.  in  some  sections.  With  ice  water,  the 


FIG.  21. — Internal  or  double-tube  cooler. 


DAIRY  INSPECTION  187 

milk  can  be  cooled  down  to  40°  F.,  while  with  ammonia 
or  brine  it  can  be  brought  still  lower,  even  to  freezing.1 
The  cooler  must  be  thoroughly  cleaned  each  time  it 
is  used,  stored  in  a  clean  place,  and  protected  from  dust 
while  in  operation,  or  the  milk  will  take  up  large  num- 
bers of  bacteria  during  the  process  of  cooling.  When  the 
cooler  is  not  properly  used  and  cared  for,  it  has  been 
found  that  better  results  can  be  obtained  by  pouring  the 
milk  directly  into  a  shipping  can  and  placing  the  can 
in  cold  water,  although  the  temperature  is  lowered  very 
slowly  under  these  conditions,  three  to  four  hours  being 
required  for  the  temperature  to  fall  to  60°  F.  In  some 
cases  it  has  been  found  more  satisfactory  to  have  the 
milk  taken  in  cans  to  the  shipping  station  and  to  cool 
it  there.  When  this  plan  is  followed  the  milk  must 
reach  the  shipping  station  during  the  period  the  germi- 

1  In  the  northern  part  of  the  United  States,  about  1%  tons 
of  ice  will  be  required  each  year  to  cool  the  milk  obtained  from 
each  cow,  while  in  the  southern  states  about  2  tons  will  be 
necessary,  allowing  for  the  waste  by  melting.  A  ton  of  packed 
ice  will  occupy  40  to  50  cubic  feet  of  space;  12  inches  should 
be  allowed  on  the  sides  and  bottom  for  sawdust  or  other  pack- 
ing material  and  3  to  4  feet  on  top  for  packing  and  ventilation. 
With  these  figures,  the  dimensions  of  an  ice  house  of  any  ca- 
pacity desired  can  be  determined.  A  foot  of  packing  material 
should  be  placed  under  the  ice  even  when  the  ice  house  has 
an  earth  floor,  earth  being  a  fairly  good  conductor  of  heat, 
especially  when  wet.  Water  from  the  melted  ice  will  usually 
drain  off  through  the  soil  unless  the  latter  is  of  clay,  in  which 
case  it  will  be  necessary  to  excavate  1  or  2  feet,  put  in  a  tile 
drain,  and  fill  in  with  gravel  or  cinders.  The  pipe  supplying 
water  to  the  milk  cooler  may  be  run  under  the  floor  of  the  ice 
house  with  advantage.  (A  number  of  good  plans  for  building 
ice  houses  will  be  found  in  the  U.  S.  Department  of  Agriculture 
Farmers'  Bulletin  No.  623.) 


188        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

cidal  power  is  active  (see  page  43).  As  a  general  rule, 
however,  it  is  best  to  run  the  milk  over  a  cooler  immedi- 
ately after  it  is  drawn  from  the  cow.  When  the  milk 
is  emptied  from  the  milk  pail  directly  into  the  tank  of  the 
cooler  and  passes  from  the  cooler  into  a  bottling  machine, 
it  is  important  to  milk  the  cows  in  such  order  that  milk 
of  low  fat  per  cent,  and  milk  of  higher  fat  per  cent, 
will  be  mixed  in  passing  through  the  bottling  machine. 

After  being  cooled,  the  milk  should  be  stored  in  a 
cool  place,  such  as  a  refrigerator,  ice-water  tank,  or 
spring  house,  until  sent  to  the  railroad  station.  The  in- 
spector should  note  the  facilities  provided  for  this  pur- 
pose. Milk  can  be  kept  cooler  in  a  tank  of  ice  water 
than  in  a  compartment  in  which  the  air  is  cooled  by  ice, 
unless  the  latter  is  well  insulated.  The  temperature 
of  air  in  an  ice-cooled  refrigerator  is  usually  not  much 
below  50°  F.,  whereas  the  temperature  of  water  in  which 
ice  is  floating  is  generally  as  low  as  40°  F.,  and  often 
lower. 

While  being  hauled  to  the  station,  the  milk  should  be 
protected  from  the  heat  in  summer.  This  is  usually 
done  by  covering  the  cans  with  a  woolen  blanket.  A 
wet  blanket  is  more  effective  than  a  dry  one.  Jackets 
of  hair  enclosed  in  canvas  are  sometimes  used  to  cover 
the  cans.  Ice  in  small  pieces  should  be  placed  in  the 
boxes  in  which  bottled  milk  is  shipped. 

The  surface  of  the  milk  cooler  and  the  inner  sur- 
face of  all  milk  vessels  should  be  examined  for  cleanli- 
ness, rusted  areas,  and  open  seams.  Uncleanliness  is 
indicated  by  an  odor  of  sour  or  putrid  milk  and  by  the 
presence  of  particles  of  coagulated  milk.  These  parti- 
cles may  be  very  small,  sometimes  no  larger  than  a  pin's 
head.  All  surfaces  with  which  milk  comes  in  contact 


DAIRY  INSPECTION  189 

should  be  covered  with  tin.  Rusted  areas  are  rough 
and  are  not  easily  cleaned,  and  they  sometimes  give  the 
milk  a  "fishy"  taste.  Milk  stored  in  rusted  vessels  will 
acquire  a  bitter,  astringent  taste  if  it  becomes  very  acid, 
in  consequence  of  the  formation  of  iron  lactate  by  the 
combination  of  the  lactic  acid  with  the  iron.  The  most 
common  location  of  rust  is  in  the  seams  and  joints,  espe- 
cially in  the  joint  between  the  bottom  and  sides.  All 
seams  should  be  filled  flush  and  smooth  with  solder. 
Seamless  vessels  are  best.  The  use  of  galvanized  iron 
buckets  for  milk  pails  should  not  be  permitted. 

Inquiry  should  be  made  in  regard  to  the  method 
of  cleaning  the  utensils  and  vessels,  including  bottles, 
and  the  facilities  provided  for  this  purpose  should  be 
noted.  The  utensils  and  vessels  should  be  first  rinsed 
with  cold  or  lukewarm  water.  If  hot  water  is  used  first, 
it  will  coagulate  the  albuminous  substances  in  the  milk 
and  cause  them  to  stick  to  the  inner  surface  of  the  vessels, 
to  the  surface  of  the  milk  cooler,  etc.  After  rinsing,  they 
should  be  washed  in  hot  water  containing  washing  soda 
or  soap  powder  and  then  rinsed  again  in  hot  water.  The 
brushes  used  in  cleaning  should  be  boiled  for  ten  min- 
utes each  time  after  they  are  used;  they  should  be  of 
good  quality  so  that  the  bristles  will  not  come  out.  The 
last  rinsing  ought  to  be  thorough,  to  insure  the  removal 
of  all  the  washing  powder,  otherwise  the  milk  may  have 
a  "fishy"  taste. 

Unclean  milk  vessels  and  utensils  are  one  of  the  most 
prolific  sources  of  bacteria  in  milk.  Particles  of  milk 
form  an  excellent  culture  media  for  bacterial  growth, 
while  the  water  used  to  wash  the  apparatus,  the  milk 
itself,  and  the  air  furnish  the  organisms  necessary  to 
start  the  growth.  The  greater  proportion  of  the  organ- 


190        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

isms  are  lactic  acid  and  putrefactive  bacteria.  Even 
when  the  vessels  and  utensils  are  thoroughly  cleansed 
in  the  manner  described,  they  still  contain  bacteria.  To 
reduce  contamination  of  milk  from  this  source  to  the 
minimum,  sterilization  is  necessary  in  addition  to  thor- 
ough washing.  The  effects  of  sterilization  are  illustrated 
by  the  investigations  of  Prucha,  Harding,  and  Weeter, 
who  found  that  the  same  milk  which  contained  515,203 
bacteria  per  c.c.  when  the  vessels  and  utensils  were 
washed  but  not  sterilized  contained  only  3875  per  c.c. 
when  the  apparatus  was  sterilized  after  washing.  Itergey 
observed  that  when  the  apparatus  was  sterilized  by  steam, 
the  character  of  the  organisms  present  in  the  milk  after 
it  had  come  in  contact  with  the  milk  pail,  strainer,  cooler, 
etc.,  did  not  differ  from  those  found  in  samples  taken 
directly  from  the  udder.  Milk  bottles  should  be  steril- 
ized before  refilling  for  the  additional  reason  that  it  is 
a  protection  against  the  infection  of  the  milk  supply  by 
bottles  which  may  be  returned  from  houses  where  infec- 
tious disease  exists. 

Exposure  to  live  steam  is  the  most  certain  method 
of  destroying  bacteria  in  milk  vessels  and  utensils.  To 
obtain  complete  sterilization,  it  is  necessary  to  expose 
the  vessels  and  apparatus  to  steam  under  5  pounds  pres- 
sure for  20  minutes.  This  is  possible  with  the  cast-iron 
sterilizers  which  can  be  tightly  closed.  Bottles  will  stand 
this  amount  of  pressure.  The  galvanized-iron  steam 
chests  frequently  used  in  dairies  are  not  sufficiently  tight 
to  hold  the  steam  under  pressure ;  in  these,  99.2  per  cent, 
of  the  bacteria  are  destroyed,  the  spore  formers  surviv- 
ing. Rinsing  or  scalding  the  vessels  and  utensils  with 
boiling  water  after  washing  does  not  destroy  many  bac- 
teria, and  while  exposure  to  the  sun  has  a  germicidal 


DAIRY  INSPECTION  191 

effect  it  also  usually  exposes  the  apparatus  to  contami- 
nation with  germ-laden  dust. 

When  facilities  for  sterilization  by  steam  are  not 
available,  the  milk  vessels  and  utensils  may  be  sterilized 
by  submerging  them  for  20  minutes  in  a  0.1  per  cent, 
solution  of  hypochlorous  acid  after  they  have  been 
cleansed  in  the  usual  way.  Hypochlorous  acid  is  even 
more  effective  as  a  germicide  than  the  hypochlorites,  al- 
though the  latter  are  150  to  200  times  as  powerful  as 
carbolic  acid.  A  0.1  per  cent,  solution  will  kill  typhoid 
bacilli  in  2%  minutes.  The  solution  may  be  conveni- 
ently prepared  as  follows:  Mix  together  equal  parts  by 
weight  of  finely  ground  commercial  bleaching  powder 
(chloride  of  lime)  and  powdered  boric  acid;  keep  in  a 
well-stoppered  bottle  and  protect  from  light.  Dissolve 
6  drams  of  the  powder  in  a  quart  of  water  by  shaking 
thoroughly,  let  stand  for  24  hours  and  pour  off  the 
clear  fluid;  then  add  4  quarts  of  water.  This  makes  a 
solution  containing  0.1  per  cent,  of  hypochlorous  acid. 
When  milk  bottles  are  submerged  in  this  solution  for 
20  minutes,  drained  for  10  to  20  minutes,  and  then  filled 
with  milk  and  capped,  no  odor  or  taste  of  chlorine  can 
be  detected  in  the  milk.  Milk  can  be  strained  through 
cheese  cloth  moistened  with  the  solution  without  any 
effect  upon  the  odor  or  taste.  Tin  vessels  are  not  cor- 
roded. The  powder  from  which  the  solution  is  pre- 
pared may  be  kept  for  some  time  under  proper  condi- 
tions, but  the  solution  rapidly  loses  strength  and  be- 
comes ineffective  in  three  weeks.  Calcium  hypochlo- 
rite  has  been  in  use  for  a  long  time  as  a  disinfectant  for 
water  supplies  and  a  solution  containing  1  ounce  to  125 
gallons  of  water  is  recommended  for  the  sterilization  of 
milk  vessels  and  utensils,  but  it  is  much  more  expensive 


192         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

than  the  hypochlorous  acid  solution.  Winslow  reports 
that  a  1  to  1000  solution  of  chloride  of  lime  may  be  used 
in  the  same  manner  and  with  the  same  results  as  the 
hypochlorous  acid  and  the  calcium  hypochlorite  solu- 
tions. 

When  milking  machines  are  in  use,  careful  inquiry 
should  be  made  regarding  the  method  of  cleaning  them. 
The  apparatus  should  be  taken  apart  each  time  after 
it  is  used  and  thoroughly  cleansed  and  sterilized.  On 
account  of  the  labor  involved,  this  is  sometimes  done 
only  once  a  day,  but  this  is  not  sufficient.  Particular 
attention  must  be  given  to  cleaning  the  metallic  and 
rubber  tubing  and  teat  cups.  After  being  rinsed  with 
cold  water  and  then  with  hot  water,  these  parts  should 
be  disinfected.  The  metallic  tubes  may  be  sterilized  by 
steam,  together  with  the  other  metallic  parts  of  the  ap- 
paratus. The  0.1  per  cent,  solution  of  hypochlorous 
acid  and  the  1  to  1000  solution  of  chloride  of  lime  are 
very  satisfactory  disinfectants  for  the  rubber  tubing  and 
teat  cups  and  for  the  metallic  parts  as  well.  The  rubber 
parts  should  be  kept  submerged  in  one  of  these  solutions 
when  not  in  use.  A  solution  of  %  pound  of  chloride 
of  lime  and  10  pounds  of  sodium  chloride  in  10  gallons 
of  water  is  also  recommended.  If  air  is  allowed  to  re- 
main in  any  part  of  the  tubing,  bacteria  may  multiply. 
The  apparatus  must  be  properly  cared  for  or  the  milk 
will  contain  a  larger  number  of  bacteria  than  when  it 
is  drawn  by  hand.  A  milking  machine  is  not  in  itself 
a  protection  against  dirt  or  bacteria  in  milk.  The  hair 
on  the  udder  around  the  teats  must  be  kept  short  and 
this  part  of  the  udder  must  also  be  cleaned  before  each 
milking  to  obtain  good  results,  while  the  teat  cups  must 


DAIRY  INSPECTION  193 

not  be  permitted  to  fall  on  the  floor  or  into  the  bedding 
when  they  become  detached  from  the  teats. 

4.  Water  Supply. — It  is  not  only  important  that 
the  water  used  on  a  dairy  farm  for  washing  the  milk 
utensils  and  vessels  shall  be  free  from  fecal  contamina- 
tion, but  also  that  the  surroundings  of  the  source  of 
supply  are  such  that  there  is  no  probability  of  contami- 
nation. While  the  first  point  can  be  decided  by  a  bac- 
teriological examination  of  a  sample  of  the  water,  the 
second  can  only  be  determined  by  an  inspection  of  the 
water  supply  and  its  surroundings.  Frequently  inspec- 
tion will  furnish  all  the  information  required  to  condemn 
a  polluted  water  supply,  but  in  many  instances  a  bac- 
teriological examination  will  be  necessary.  The  exami- 
nations reported  of  farm  water  supplies  indicate  that 
they  are  frequently  contaminated. 

On  many  farms  the  water  supply  is  obtained  from 
springs  or  from  dug  wells.  In  either  case,  the  source 
of  supply  is  the  underground  water.  A  well  is  an  arti- 
ficial opening  from  the  surface  down  to  the  underground 
water,  while  a  spring  is  a  place  where  the  underground 
water  has  come  to  the  surface.  The  underground  water 
is  contained  in  the  interstices  between  rocks,  gravel,  sand, 
clay,  etc.,  at  various  depths  below  the  surface  of  the 
ground.  The  level  of  the  underground  water,  i.e.,  the 
water  table,  conforms  in  a  general  way  to  the  level  of 
the  ground  surface  (Fig.  22). 

The  purity  of  spring  water  depends  very  largely 
upon  the  location  of  the  spring.  When  springs  on  farms 
are  contaminated,  it  is  usually  due  to  pollution  by  sur- 
face wash  or  subsurface  drainage.  A  dry  closet  situated 
on  the  slope  of  a  hill  above  a  spring  is  especially  dan- 
gerous. The  location  of  manure  piles,  houses,  barns,  pig 

13 


194        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

pens,  or  other  structures  above  springs  is  objectionable. 
Water  from  springs  exposed  to  surface  drainage  should 
not  be  used  for  washing  dairy  utensils  and  vessels,  but 
if  no  other  source  is  available  the  spring  should  be  pro- 
tected by  impervious  walls.  Open  springs  are  sometimes 
polluted  by  live  stock  or  contaminated  by  dust,  leaves, 
and  other  refuse  blowing  into  them.  Pollution  of  springs 
by  subsurface  drainage  is  not  very  common  on  farms, 
but  may  occur  where  the  layer  of  earth  above  the  water 
table  is  thin  or  readily  permeable.  The  permeability  will 
depend  upon  the  material  present.  Fine  sand  is  a  good 


Fia.  22. — Section  showing  relation  of  water  table  to  surface  irregularities.     (From  Water 
Supply  Paper  255,  U.  S.  Geological  Survey.) 

filter,  but  coarse  sand  and  gravel  permit  the  water  to 
pass  through  rapidly,  carrying  some  of  the  contaminat- 
ing material  through  with  it.  Clay  and  till  (largely  clay 
and  sand)  are  good  filters.  When  the  layer  of  earth 
above  the  water  table  is  thin  or  permeable,  the  water  in 
the  spring  is  likely  to  be  warm.  Cesspools,  buildings, 
or  anything  else  which  may  be  a  source  of  pollution 
should  not  be  placed  at  a  higher  level  than  a  spring  be- 
cause of  the  danger  of  contamination  by  subsurface 
drainage  (Fig.  23).  When  cracks  or  fissures  extend 
from  the  surface  into  the  water-bearing  strata,  as  occurs 
in  rock  formation,  or  where  tubular  channels  have  been 
formed,  the  spring  may  be  contaminated.  This  may 


DAIRY  INSPECTION  195 

occur  especially  in  limestone  districts,  in  which  basins  or 
sinks  may  be  found  on  the  surface  which  are  connected 
with  underground  water  channels.  Muddy  water  or 
floating  material  in  the  spring  after  severe  rains  are 
indications  of  the  existence  of  these  conditions. 

The  safety  of  well  water  depends  upon  the  purity  of 
the  water  at  its  source,  which  is  the  underground  water* 
and  the  protection  provided  against  the  entrance  into  the 
well  of  contaminated  water  or  polluting  material.  The 
purity  of  the  underground  water  in  the  case  of  a  well 
will  depend  upon  the  same  conditions  as  control  the 
purity  of  springs.  Contaminated  water  or  polluting 


Cesspool 


FIG.  23. — How  springs  may  be  polluted  by  subsurface  drainage.      (From  Water  Supply 
Paper  255,  U.  S.  Geological  Survey.) 

material  may  enter  the  well  through  openings  in  the 
curbing  or  casing  and,  in  open  wells,  from  the  surface 
also. 

The  open  or  dug  well  is  the  type  most  commonly 
found  on  farms  because  it  is  the  most  cheaply  made  and 
the  work  can  be  done  by  ordinary  farm  labor.  With 
certain  precautions,  the  dug  well  yields  a  satisfactory 
supply  of  water,  but  as  commonly  constructed  it  is  the 
most  dangerous  of  all  sources  of  water  supply.  A  dug 
well  may  be  contaminated  by  material  seeping  through 
the  ground  and  curbing,  or  entering  from  the  top. 
Stone,  brick,  or  wood  curbing  usually  contains  crevices 
which  permit  the  passage  of  polluting  material.  Such 


196         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

material  may  also  enter  through  leaks  or  holes  in  the  iron 
casing  of  drilled  wells.  Cesspools  and  privies  are  the 
most  common  sources  of  seepage.  Material  thrown  out 
upon  the  surface  of  the  ground  may  also  be  carried  down 
through  the  soil  by  rain  and  seep  into  the  well  or  reach 
the  underground  water.  The  "safety  distance"  from 
such  sources  of  pollution  will  depend  upon  the  character 
of  the  soil  and  the  quantity  and  concentration  of  the 
polluting  material,  but  a  rule  that  may  serve  as  a  gen- 
eral guide  is  the  following:  A  well  drains  an  inverted 
cone  of  land  whose  top  surface  is  four  times  as  wide  as 
the  depth  of  the  well.  Stone  or  brick  curbs  may  be  made 
impervious  by  covering  the  interior  surface  with  cement. 
This  will  prevent  contamination  by  seepage  unless  the 
well  is  shallow,  in  which  case  the  polluting  material  may 
pass  down  and  enter  the  well  under  the  bottom  of  the 
curb. 

One  of  the  most  common  methods  of  pollution  of 
dug  wells  is  the  entrance  of  material  through  the  top. 
Dust  and  surface  washings  from  pump  drippings,  waste 
water,  and  rains  are  the  principal  sources  of  contami- 
nation. Small  animals,  such  as  toads,  mice,  rats,  moles, 
and  snakes,  fall  into  open  wells  in  seeking  water  in  pe- 
riods of  drought.  A  water-tight  iron  or  cement  cover, 
tightly  joined  to  the  curb,  will  protect  the  well  from 
these  surface  contaminations. 

Deep  wells,  driven  or  bored,  are  less  likely  to  be  pol- 
luted than  dug  wells  or  shallow  bored  wells  because  the 
underground  water  is  protected  from  seepage  by  a  much 
thicker  stratum  of  earth  and  the  well  is  protected  by  an 
iron  casing.  If  cracks  or  leaks  occur  in  the  casing,  pol- 
luting material  may  enter.  While  deep  wells  are  subject 
to  contamination,  they  are  a  much  safer  source  of  water 
supply  than  shallow  wells. 


DAIRY  INSPECTION  197 

V.    SCORE  CABDS 

It  is  important  to  have  some  system  of  recording 
the  conditions  found  on  inspection  by  which  the  dairy 
farm  can  be  rated  and  classified  according  to  a  certain 
standard.  Comparisons  can  then  be  made,  when  desired, 
between  different  dairy  farms  and  also  of  the  condition 
of  the  same  farm  at  different  times.  In  addition,  the 
rating  or  classification,  together  with  the  details  of  the 
record,  will  serve  as  a  basis  for  an  opinion  as  to  the  qual- 
ity of  milk  which  may  be  expected  from  each  farm.  These 
ratings,  or  scores,  if  published,  will  also  serve  as  a  guide 
to  the  consumer  in  purchasing  milk. 

The  most  satisfactory  system  of  this  kind  is  what  is 
known  as  the  score-card  method.  In  this  method,  100 
is  taken  as  a  perfect  score  and  various  portions  of  this 
number  are  assigned  to  different  parts  of  the  equip- 
ment and  methods,  according  to  what  is  considered  to 
be  the  relative  importance  of  each.  Each  part  of  the 
equipment  and  the  various  methods  are  rated  or  scored 
by  the  inspector  according  to  the  degree  with  which  they 
meet  the  standard  of  perfection,  and  the  total  of  these 
figures  constitutes  the  score  for  the  dairy  farm.  Sev- 
eral kinds  of  score  cards  are  in  use.  There  is  one  pre- 
pared by  Dr.  W.  C.  Woodward,  health  officer  of  the 
District  of  Columbia,  the  originator  of  the  score-card 
system.  A  score  card  prepared  by  Prof.  Raymond 
Pearson,  known  as  the  Cornell  score  card,  and  another 
published  by  the  U.  S.  Bureau  of  Animal  Industry  are 
also  in  rather  general  use.  These  three  score  cards  are 
printed  on  the  following  pages: 


198        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

(Front  of  Card) 
HEALTH  DEPARTMENT  OF  THE  DISTRICT  OP  COLUMBIA 

SCORE  CARD  FOR  DAIRY  FARMS 
Farm  of Location 

APPermit°n}Number Consignee 

Date 

This  score  card  shows  conditions  only  at  the  time  of  this  inspection.  To  learn  of  conditions 
erally  prevailing,  reference  should  be  made  to  a  series  of  consecutive  score  cards.  This  may  be  < 
at  the  Health  Office. 


Sec 

>re 

Sc 

ore 

A.    STABLE  AND    YARD 

Per- 
fect 

Al- 
lowed 

Per- 
fect 

Al- 
lowed 

1    Stable*    Site    well  drained    and 

Total  brought  forward.  .  ..... 

30 

free  from  contaminating  sur- 

1 

B.  MILK  HOUSE 

2.  Construction  of  stable: 

1.  Site:     Free  from  contaminating 
surroundings,     with     separate 
wash  rooms  

1 

3 

1 

Smooth,  tight  walls  and  ceiling 

2 

3.  Construction  of  floor,  walls,  and 

1 

3.  Light:    Four  sq.  ft.  or  more  of 
glass  per  cow,   and  adequate 
artificial  lighting  for  milking.  . 
(Three  sq.  ft.,  2;  two  Sq.  ft.,  1.) 

3 

2 

4.  Light,  ventilation,  and  screens  .  . 
5.  Cleanliness    of    milk    room,    in- 
cluding freedom  from  flies  

C.   UTENSILS 

1 
3 

10 

(Adjustable  windows,  1.) 
Cubic  feet  of  air  space  per  cow, 
1  000  to  600         

2 

(Removable  top,  5.) 
2.  Facilities  for  sterilization  
(Steam,  10;  boiling  water,  5.) 

10 

(500  to  600,  1.) 
Stable  air 

2 

3.  Thorough  cleansing  and  steriliz- 
ing of  utensils  

10 

4.  Milk  cooler      

1 

5.  Cleanliness: 

2 

5.  Construction: 
Sound,  of  good  type,  and  in 

1 

Walls               

1 

6.  Water  for  cleaning,  clean,  con- 

1 

2 

Mangers  and  partitions  
Windows            

1 
1 

D.  MILKING  AND   MILK 

Bedding 

2 

1.  Udders  washed  and  dried 

6 

6.  Water  for  cattle:  Clean  and  fresh 

1 

(Cleansed  with  moist  cloth,  2.) 
2.  Attendants:    Cleanliness  and  ap- 

2 

7.  Yard*    Free  from  manure,  clean 

2a.  Med.  Insp.  Employees  

3 

2 

1 

(Manure  stored  less  than  50 
feet  from  stable,  0.) 

4.  Milk  of   each  cow  removed  im- 
mediately from  stable  

2 
4 

8.  Privy: 

(To  include   accommodations 
for  employees.) 

1 

6.  Efficient  cooling  ;  below  50°  F  ... 
(51°  F.  to  55°  F.,  2;  56°  F.  to 
60°  F.,  1.) 
7.  Storage-  below  50°  F  

5 
3 

1 

3 

1 

(Jacket  or  wet  blanket,  2;  dry 

Disposal  of  Contents  

1 

blanket  or  covered  wagon,  1.) 

Total  carried  forward 

30 

Total        

100 

Remarks . . 


Source  of  water  supply General  condition  of  farm. 

Violation  of  regulations,  Sec of  Milk  Act,  Sec 

Notices  served,  to  correct,  to  show  cause  by 


Inspector. 


DAIRY  INSPECTION 

(Back  of  Card) 

HEALTH  DEPARTMENT  OF  THE  DISTRICT  OP  COLUMBIA 
SCORE  FOR  CATTLE 


199 


Number  of  cattle  in               Perfect  score, 
dairy  herd                      For  each  cow          Total  possible  score  for  herd  
or  bull,  100 

Deductions  on  account  of  cattle  diseased,  etc. 

Number  of 
Cattle 

Nature  of  disease,  defect,  etc. 

Deductions 
per  cow 

Total 
Deductions 

1.  Tuberculosis  as  shown  by  a  physical 
examination,  or  by  the  tuberculin 
test  

100 

30 
100  or  less 

100  or  less 
40  or  less 

30  or  less 
10  or  less 

2.  Absence  of  a  tuberculin  test  within 
one  year  of  the  date  of  inspection, 
not  to  include  cattle  scored  under 
paragraph  1  

3.  Inflammatory  diseases  of  the  udder.  . 
4.  Diseases  other  ttian  or  in  addition  to 
the  diseases  mentioned  above  

5.  Unclean  condition  of  the  teats  and 
udders  

6.  Unclean  condition  of  the  cows  other 
than  spepified  in  the  preceding  par- 
agraph. . 

7.  Undue  emaciation  or  cows  otherwise 
out  of  condition.  .  . 

Total  deductions  for  herd 


Net  score 
Net  score  (  )  divided  by  the  total  possible  score 

for  herd  (  )  equals        Percentage  score 


Remarks. 


Inspector. 

The  Health  Department  believes  that  if  a  cow  is  suffering  from  tuberculosis, 
her  entire  value  as  a  dairy  cow  is  gone.  If  she  is  suffering  from  an  inflammatory 
disease  of  the  udder  as  well  as  from  tuberculosis,  she  becomes  even  a  greater  danger 
to  the  herd.  And  if  she  is  furthermore  otherwise  diseased,  or  out  of  condition,  or 
dirty,  she  becomes  even  a  more  serious  menace  to  public  health.  For  these  reasons, 
the  above  system  of  scoring  has  been  arranged  so  that  an  individual  cow  may 
count  against  the  score  of  the  entire  herd  more  than  would  have  been  allotted  to 
her  had  she  been  in  perfect  condition. 

All  cows  stabled  with  the  dairy  herd  or  found  in  the  milking  line  will  be  scored 
as  part  of  the  herd. 


200        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

(Front  of  Card) 

UNITED    STATES    DEPARTMENT    OF    AGRICULTURE,    BUREAU    OP    ANIMAL    INDUSTRY 

DAIRY  DIVISION 


SANITARY  INSPECTION  OF  DAIRY  FARMS 


SCORE   CARD 

Owner  or  lessee  of  farm 

P.  O.  address State 

Total  number  of  cows Number  milking 

Gallons  of  milk  produced  daily 

Product  is  sold  by  producer  in  families,  hotels,  restaurants,  stores,  to 

dealer. 

For  milk  supply  of 

Permit  No Date  of  inspection ,191 

REMARKS: 


(Signed) 

Inspector. 


DAIRY  INSPECTION 

(Back  of  Card) 


201 


Equipment 

Score 

Methods 

Score 

Per- 
fect 

Al- 
lowed 

Per- 
fect 

Al- 
lowed 

cows 
Health 

6 

1 

1 

2 
4 

4 

cows 
Clean  .       ...                       

8 
6 

5 
I 

Apparently  in  good  health  1 
If  tested  with  tuberculin  within 
a  year  and  no  tuberculosis  is 
found,  or  if  tested  within  six 
months  and  all  reacting  ani- 
mals removed  5 

(Free  from  visible  dirt,  6.) 

STABLES 

Floor                                              2 



Walls                                                1 

(If  tested  within  a  year  and  re- 
acting animals  are  found  and  re- 
moved, 3.) 

Mangers  and  partitions  1 
Windows  1 

Water  (clean  and  fresh)  

Stable  air  at  milking  time  

STABLES 

2 
2 

Well  drained                                   1 

Clean                                               1 

Free  from  contaminating  sur- 
roundings    1 

Well  drained  1 
Removal  of  manure  daily  to  50  feet 

Tight,  sound  floor  and  proper 
gutter                               .  .    .  2 

MILK  BOOK   OR   MILK  HOUSE 

Smooth,  tight  walls  and  ceilings  1 
Proper  stall,  tie,  and  manger  ...  1 
Provision  for  light:    Four  sq.  ft.  of 

UTENSILS  AND    MILKING 

Care  and  cleanliness  of  utensils  
Thoroughly  washed        2 

8 
9 

2 
2 

2 
5 

8 

2 

(Three  sq.  ft.,  8;  2  sq.  ft.,  2;  1  sq. 
ft.,   1.    Deduct  for  uneven  distri- 
bution.) 
Bedding  

1 



Sterilized  in  steam  for  15  min- 
utes                             8 

Ventilation 

7 

1 
1 

5 
1 

1 

(Placed  over  steam  jet,  or  scalded 
with  boiling  water,  2.) 
Protected  from  contamination.  .8 
Cleanliness  of  milking  

Provision  for  fresh  air,  control- 
able  flue  system  8 

(Windows  hinged  at  bottom, 
1.5;    sliding    windows,    1; 
other  openings,  0.5.) 
Cubic  feet  of  space  per  cow,  500 
ft  3 

Udders   washed  and  wiped  ....  6 
(Udders  cleaned  with  moist  cloth, 
4;  cleaned  with  dry  cloth  or  brush 
at  least  15  minutes  before  milking, 
1.) 

HANDLING   THE   MILK 

Cleanliness   of  attendants  in   milk 
room  

(Less  than  500  ft.,  2;  less  than 
400  ft.,  1;  less  than  800  ft.,0.) 
Provision  for  controlling  tem- 
perature                                    1 

UTENSILS 

Construction  and  condition  of  uten- 
sils   

Milk    removed    immediately    from 
stable  without  pouring  from  pail  .  . 
Cooled  immediately   after   milking 

Water  for  cleaning  

(Clean,  convenient,and  abundant.) 
Small-top  milking  pail  

Cooled  below  50°  F 



Milk  cooler 

(51°  to  55°,  4;  56°  to  60°,  2.) 
Stored  below  50°  F  
(51°  to  65°,  2;  56°  to  60°,  1.) 
Transportation  below  50°  F  
(51*  to  55°,  1.5;  56°  to  60°,  1.) 
(If  delivered  twice  a  day,  allow 
perfect  score  for  storage  and  trans- 
portation.) 

Total 

Clean  milking  suits  

MILK  ROOM  OR  MILK  HOUSE 

Location:  Free  from  contaminating 

Construction  of  milk  room  
Floor,  walls,  and  ceilings  1 
Light,  ventilation,  screens  ....  1 
Separate  rooms  for  washing  utensils 
and  handling  milk 

2 
1 

Facilities  for  steam  

1 



(Hot  water,  0.5.) 
Total  

40 



60 

Equipment +Methods = Final   Score. 

NOTE  1. — If  any  exceptionally  filthy  condition  is  found,  particularly  dirty  utensils,  the  total  score 
may  be  further  limited. 

NOTE  2. — If  the  water  is  exposed  to  dangerous  contamination,  or  there  is  evidence  of  the  presence 
of  a  dangerous  disease  in  animals  or  attendants,  the  score  shall  be  0. 


202        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 


DEPARTMENT  OF  DAIRY  INDUSTRY,  COLLEGE  OF  AGRICULTURE, 
CORNELL  UNIVERSITY 


SCORE  CARD  FOR  PRODUCTION  OF  SANITARY  MILK 


Date. 


Dairy  of. 


Per- 
fect 

Score 

I.  Health  of  the 
herd  and  its 

Health  and  comfort  of  the  cows  and  their  isola- 
tion when  sick  or  at  calving  time 

45 

protection 

Location,  lighting  and  ventilation  of  the  stable  . 
Food  and  water  

35 
20 

Total  

100 

II.  Cleanliness    of 

Cows  

30 

the  cows  and 

Stable  

20 

thei  r    sur- 

20 

roundings 

Stable  air  (freedom  from  dust  and  odors) 

30 

Total 

100 

III.  Construction 
and  care  of 

Construction  of  utensils  and  their  cleaning  and 
sterilizing 

40 

the  utensils 

Water  supply  for  cleaning  and  location  and  pro- 

25 

Care  of  utensils  after  cleaning  .  . 

20 

Use  of  small-top  milking  pail    ... 

15 

Total 

100 

IV.  Health  of  em- 

Health of  employees.  .          .          .          .    . 

45 

ployees   and 
manner      of 

Clean  over-all  milking  suits  and  milking  with 
clean,  dry  hands  

30 

milking 

Quiet  milking,  attention  to  cleanliness  of  the 
udder  and  discarding  fore-milk 

25 

Total 

100 

V.  Handling     the 

Prompt  and  efficient  cooling  

35 

milk 

Handling  milk  in  a  sanitary  room  and  holding  it 
at  a  low  temperature 

35 

Protection  during  transportation  to  market  .... 

30 

Total  

100 

TOTAL  OF  ALL  SCORES  

500 

If  the  total  of  all  scores  is 

480  or  above 

450  or  above 

400  or  above 

Below  400. .. 


And  each  division  is        The  sanitary  conditions  are 

...  90  or  above EXCELLENT 

...  80  or  above GOOD 

...  60  or  above MEDIUM 

...  Or  any  division  is  below  60 POOR 


The  sanitary 

conditions  are . 


Scored  by. 


CHAPTER   VIII 

PASTEURIZATION 

Pasteurization  of  milk  consists  in  heating  the  milk 
at  various  temperatures  below  boiling  for  a  variable 
period  of  time.  The  term  pasteurized  milk  is  very  indefi- 
nite in  its  meaning  because  the  process  is  not  always  car- 
ried out  in  the  same  manner,  but  since  1913,  when  the 
Commission  on  Milk  Standards  of  the  New  York  Milk 
Committee  published  its  second  report,  there  has  been 
more  uniformity  in  this  country  than  formerly  with  re- 
gard to  temperature  and  time  of  exposure,  state  and 
local  authorities  having  very  generally  accepted  the 
standard  adopted  by  the  Commission.  This  standard 
specifies  140  to  155°  F.  (60  to  68°  C.)  as  the  minimum 
temperature  at  which  the  milk  shall  be  heated,  the  mini- 
mum period  of  exposure  to  be  20  minutes  at  140°  F. 
(60°  C.),  with  one  minute  less  for  each  degree  of  tem- 
perature above  140°  F.  But,  at  the  same  time,  in  order 
to  allow  for  the  variations  in  temperature  and  holding- 
time  which  may  occur  under  commercial  conditions,  the 
Commission  recommended  that  the  milk  be  heated  to 
at  least  145°  F.  (62.8°  C.)  for  at  least  30  minutes.  In 
Europe,  pasteurized  milk  is  usually  milk  which  has  been 
heated  for  a  few  moments  at  176°  F.  (80°  C.)  or  above, 
although  within  recent  years  the  method  of  heating  the 
milk  at  a  lower  temperature  for  a  longer  period  has 
been  adopted  to  some  extent. 

When  the  first  commercial  milk  pasteurizer  was  in- 
troduced into  this  country  in  1895,  pasteurization  was 
recommended  to  milk  distributers  as  a  means  of  pre- 
203 


204        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

venting  milk  from  spoiling,  and  the  process  was  adopted 
by  some  dealers  for  this  purpose,  being  used  secretly  by 
many  of  them.  Naturally,  this  brought  the  process  into 
disrepute.  Sanitarians  and  public  health  authorities  were 
also  disposed  to  discourage  its  use  because  of  the  ineffi- 
ciency of  the  early  apparatus  and  the  lack  of  exact  in- 
formation regarding  the  effect  of  the  process  upon  the 
milk  and  the  pathogenic  organisms  which  may  be  con- 
tained in  it.  With  the  acquirement  of  further  informa- 
tion on  the  latter  phase  of  the  subject  and  improvement 
of  the  apparatus,  sanitarians  and  public  health  officials 
came  to  regard  the  pasteurization  of  milk,  when  prop- 
erly carried  out,  as  a  legitimate  and  useful  process  and 
by  1910  the  pendulum  had  swung  so  far  in  the  other 
direction  that  many  of  them  were  advocating  the  pas- 
teurization of  all  milk. 

PRINCIPLES  OF  PASTEURIZATION 

To  obtain  a  correct  conception  of  the  hygienic  value 
of  pasteurization,  it  is  necessary  to  consider  the  effect  of 
different  degrees  of  heat  and  periods  of  exposure  upon 
the  pathogenic  organisms  which  may  be  present  in  the 
milk,  upon  the  common  milk  bacteria,  upon  the  toxins 
and  decomposition  products  resulting  from  bacterial 
growth,  upon  the  nutritive  properties  of  the  milk,  and 
upon  the  ferments  or  enzymes.  Commercially,  the  effect 
upon  the  taste  and  the  separation  of  the  cream  is  also 
of  importance. 

1.  Effect  of  Heat  on  Pathogenic  Organisms. — The 
disease-producing  bacteria  which  occur  most  frequently 
in  milk  are  streptococci,  the  bacilli  of  tuberculosis,  ty- 
phoid fever  and  diphtheria,  and  the  pyogenic  staphylo- 
cocci.  The  infectious  agent  of  scarlet  fever,  which  is 


PASTEURIZATION  205 

also  sometimes  transmitted  by  milk,  has  not  been  iden- 
tified. Of  the  organisms  mentioned,  the  tubercle  bacillus 
is  the  most  resistant  to  heat,  with  the  possible  exception 
of  some  varieties  of  streptococci.  The  streptococci  of 
septic  sore  throat  are  destroyed  by  heating  at  140°  F. 
(60°  C.)  for  ao  minutes  (Davis)  or  at  145°  F.  (62.8° 
C.)  for  20  minutes  (Hamburger),  and  exposure  to  a 
temperature  of  125.6  to  143.6°  F.  (52  to  62°  C.)  for 
30  minutes  is  sufficient  to  kill  Streptococcus  pyogenes 
(Kitchens).  There  are  some  varieties  of  streptococci 
which  are  more  resistant  to  heat,  but  we  have  no  reason 
to  believe  that  those  which  occur  in  milk  are  pathogenic. 
It  seems  very  probable  that  heating  milk  sufficiently  to 
destroy  tubercle  bacilli  will  also  kill  any  pathogenic  strep- 
tococci which  may  be  present.  A  temperature  of  140°  F. 
(60°  C.)  for  2  minutes  will  destroy  the  bacilli  of  typhoid 
fever  and  diphtheria.  The  question  of  the  amount  of 
heat  required  to  destroy  the  pathogenic  organisms  which 
occur  most  frequently  in  milk  consequently  resolves  it- 
self into  a  question  of  how  much  heat  is  necessary  to  kill 
the  tubercle  bacillus.  The  evidence  on  this  point  must 
therefore  be  considered. 

Bang  found  that  heating  milk  momentarily  at  185° 
F.  (85°  C.)  destroyed  tubercle  bacilli  in  naturally  in- 
fected milk,  and  Jensen  reports  experiments  in  which 
tubercle  bacilli  in  milk  were  killed  by  a  few  moments 
exposure  to  158  to  176°  F.  (70  to  80°  C.) .  On  the  other 
hand,  Grimmer  and  6ther  investigators  are  of  the  opinion 
that,  when  the  exposure  is  momentary,  a  temperature  of 
at  least  194° (F.  (90°  C.)  is  necessary  to  insure  the  de- 
struction of  the  bacilli  in  all  cases. 

Concerning  the  effects  of  a  more  prolonged  exposure 
at  lower  temperatures,  experimental  results  are  even 


206        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

more  divergent.  Woodhead  reports  that  while  in  some 
experiments  a  temperature  of  140°  F.  (60°  C.)  killed 
tubercle  bacilli  in  25  minutes,  in  others  an  exposure  of 
8  hours  was  required.  Yersin,  Bitter,  Bonhoff,  and  other 
investigators  report  that  although  an  exposure  to  140° 
F.  (60°  C.)  for  one  hour  was  nearly  always  fatal  to 
tubercle  bacilli,  the  effect  was  uncertain  when  the  time 
of  exposure  was  much  shorter.  In  Foster  and  Rull- 
mann's  experiments,  the  bacilli  remained  alive  after  45 
minutes  at  140°  F.  (60°  C.).  DeJong  asserts  that  tu- 
bercle bacilli  will  survive  heating  at  159.8  to  161.6°  F. 
(71  to  72°  C.)  for  y2  hour,  while  Van  der  Sluis  de- 
clares that  a  temperature  of  176°  F.  (80°  C.)  for  1  hour 
is  necessary  to  kill  tubercle  bacilli  in  naturally  infected 
milk.  Hittcher  considers  1  hour  at  140  to  145.4°  F.  (60 
to  63°  C.) ,  45  minutes  at  147.2  to  149°  F.  (64  to  65°  C.) , 
or  30  minutes  at  150.8  to  158°  F.  (66  to  70°  C.)  neces- 
sary to  destroy  tubercle  bacilli.  On  the  other  hand,  Hew- 
lett, in  England,  found  that  tubercle  bacilli  did  not  sur- 
vive 30  minutes  exposure  to  140°  F.  (60°  C.)  and,  in 
this  country,  Rosenau  found  20  minutes  at  140°  F., 
Theobald  Smith  15  minutes  at  140°  F.,  and  Russell  and 
Hastings  10  minutes  at  that  temperature  sufficient  to 
kill  the  organisms.  Hewlett  and  the  American  investi- 
gators used  in  their  experiments  milk  artificially  in- 
fected with  tubercle  bacilli,  while  nearly  all,  if  not  all, 
of  the  other  experiments  mentioned  were  made  with 
naturally  infected  milk. 

The  conditions  were  therefore  by  no  means  the  same. 
In  naturally  infected  milk,  the  tubercle  bacilli  are  em- 
bedded in  masses  of  mucus,  clots  of  fibrin,  or  shreds  of 
tissue,  and  this  albuminous  covering  protects  them  from 
the  action  of  the  heat.  It  is  true  that  in  those  experi- 


PASTEURIZATION  207 

ments  in  which  milk  from  tuberculous  udders  was  used 
without  being  diluted  with  normal  milk  that  the  circum- 
stances were  not  the  same  as  exist  under  natural  condi- 
tions; the  infection  was  much  more  concentrated,  and 
there  was  not  the  same  opportunity  for  the  albuminous 
matter  surrounding  the  bacilli  to  be  softened  and  loos- 
ened as  occurs  when  a  small  quantity  of  infected  milk 
is  mixed  with  a  comparatively  large  quantity  of  normal 
milk  several  hours  before  pasteurization.  But  individual 
milk  was  not  used  in  all  of  the  experiments  with  natu- 
rally infected  milk;  some  of  them  were  made  with  mixed 
milk  which  was  entirely  normal  in  appearance. 

In  all  of  the  experiments  referred  to  a  small  quantity 
of  milk  was  heated  in  a  laboratory.  Under  these  condi- 
tions, the  temperature  at  which  the  milk  is  heated  and 
the  time  of  exposure  can  be  accurately  controlled.  But 
in  commercial  pasteurizers  fluctuations  in  temperature 
and  variations  in  holding- time  cannot  be  entirely  avoided 
and  when  large  quantities  of  milk  are  pasteurized  under 
these  conditions  there  is  not  the  same  assurance  that  every 
particle  of  milk  will  be  heated  at  the  same  temperature 
for  the  same  length  of  time  as  when  a  small  quantity  of 
milk  is  heated  in  the  laboratory.  This  is  shown  by  the 
experiments  of  Rosenau  and  Schorer  in  which  they  tested 
the  efficiency  of  pasteurization  under  commercial  condi- 
tions. They  inoculated  milk  with  cultures  of  the  bacilli 
of  typhoid  fever,  diphtheria,  and  tuberculosis  and  en- 
deavored to  heat  it  at  140  to  145°  F.  (60  to  62.8°  C.) 
for  different  periods  of  time.  Two  tests  were  made  with 
typhoid  bacilli  and  in  one  the  organisms  survived.  The 
same  results  were  obtained  with  the  diphtheria  bacillus. 
In  two  tests  with  tubercle  bacilli  of  the  bovine  type  one 
failed,  and  in  a  similar  experiment  with  tubercle  bacilli 


208        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

of  the  human  type  the  organisms  were  not  killed  in  either 
test.  As  a  result  of  these  experiments,  Rosenau  and 
Schorer  concluded  that  in  order  to  allow  a  margin  of 
safety  when  milk  is  pasteurized  under  commercial  condi- 
tions it  is  necessary  to  expose  the  milk  to  a  temperature 
of  at  least  145°  F.  (62.8°  C.)  for  30  to  45  minutes. 

The  only  experiment  recorded  in  which  naturally 
infected  milk  was  pasteurized  in  large  quantity  under 
commercial  conditions  was  made  by  Traum  and  Hart, 
who  published  their  results  in  1916.  The  milk  came 
from  a  large  herd  of  reacting  cows  and  the  volume 
amounted  to  from  700  to  1000  quarts  daily.  Samples 
were  taken  at  the  milk  station  in  the  city  before  and  after 
pasteurization.  Twenty- four  samples  of  raw  milk  were 
tested  on  guinea  pigs  and  all  except  one  sample  produced 
tuberculosis  in  the  test  animals,  and  the  guinea  pigs  inoc- 
ulated with  this  sample  died  of  septicemia  before  there 
was  an  opportunity  for  tuberculosis  to  develop.  Eleven 
samples  of  milk  which  had  been  heated  at  140°  F.  (60° 
C.)  for  20  minutes  were  tested  in  the  same  manner  and 
did  not  produce  tuberculosis  in  a  single  instance.  Twelve 
samples  of  milk  which  had  been  heated  above  140°  F. 
(60°  C.)  for  a  longer  period  than  20  minutes  also  proved 
free  from  tuberculosis  infection.  While  these  results  ap- 
pear to  indicate  that  140°  F.  (60°  C.)  for  20  minutes 
will  kill  tubercle  bacilli  in  naturally  infected  milk  when 
it  is  pasteurized  under  commercial  conditions,  it  would 
seem  desirable,  in  view  of  the  contradictory  data  fur- 
nished by  the  other  experiments  which  have  been  men- 
tioned, to  have  them  confirmed  by  further  tests  before 
drawing  final  conclusions.  There  ought  to  be  absolute 
certainty  that  a  given  temperature  and  period  of  expo- 
sure will  kill  tubercle  bacilli  and  other  pathogenic  organ- 


PASTEURIZATION  209 

isms  in  naturally  infected  milk  before  they  are  adopted 
as  a  standard  for  pasteurized  milk. 

2.  Effect  of  Heat  on  the  Common  Milk  Bacteria. — 
The  effect  of  pasteurization  upon  the  common  milk  bac- 
teria is  of  importance  because  if,  for  example,  the  lactic 
acid  bacteria  are  destroyed  and  peptonizing  or  gas-form- 
ing organisms  survive  the  milk  may  undergo  putrefac- 
tion instead  of  souring.  Moreover,  the  putrefactive 
changes  may  advance  sufficiently  to  render  the  milk  in- 
jurious before  the  appearance  or  taste  is  altered. 

The  action  of  different  degrees  of  heat  upon  the  com- 
mon milk  bacteria  has  been  very  thoroughly  studied  by 
Ayers  and  Johnson.  In  their  experiments,  when  milk 
was  heated  to  170°  F.  (76.7°  C.)  or  above,  the  majority 
of  the  organisms  surviving  were  peptonizers,  but  when 
the  temperature  was  kept  below  170°  F.  the  acid-formers 
predominated  among  the  surviving  organisms.  Acid 
was  formed  slowly,  however,  when  the  temperature  had 
reached  160°  F.  (71.1°  C.).  The  character  of  the 
changes  which  the  milk  will  undergo  after  pasteuriza- 
tion will  depend  not  only  upon  the  kind  of  bacteria  which 
predominate  after  heating,  but  also  upon  the  tempera- 
ture at  which  the  milk  is  kept.  If  pasteurized  milk  is 
not  cooled  promptly  and  kept  cool  it  undergoes  putre- 
faction, especially  if  it  has  been  exposed  to  high  degrees 
of  heat.  Milk  heated  at  a  low  temperature,  145°  F. 
(62.8°  C.)  for  30  minutes,  when  kept  at  50 °  F.  (10°  C.), 
will  curdle  and  sour  like  raw  milk,  but  much  more  slowly. 
If  milk  treated  in  this  manner  is  stored  too  long,  it  may 
develop  a  strong,  old  taste  as  a  result  of  the  growth  of 
the  alkali- forming  bacteria  which  survive  this  amount 
of  heat. 

Pasteurization  destroys  or  weakens  the  germicidal 

14 


210        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

power  of  milk.  It  was  therefore  naturally  supposed  that 
bacteria  would  develop  more  rapidly  in  pasteurized  than 
in  raw  milk.  Rickards  compared  the  average  increase 
of  bacteria  occurring  in  a  number  of  samples  of  raw  and 
pasteurized  milk  and  found  that  bacteria  multiplied  four 
times  faster  in  commercially  pasteurized  milk  than  in 
raw  milk  at  ice-box  temperature.  Ayers  and  Johnson 
contend,  however,  that  when  the  growth  of  bacteria  in 
pasteurized  milk  is  compared  with  the  growth  of  bacteria 
in  the  same  grade  of  raw  milk  the  increase  of  bacteria 
is  about  the  same  in  both  kinds  of  milk.  But  Savage 
is  of  the  opinion  that  organisms  which  gain  access  to 
milk  after  pasteurization  will  grow  more  rapidly  than  in 
raw  milk  if  for  no  other  reason  than  because  the  bac- 
terial content  is  much  less  and  the  conditions  for  growth 
therefore  much  more  favorable.  These  facts  illustrate 
the  importance  of  promptly  cooling  pasteurized  milk  and 
keeping  it  cool,  and  also  indicate  the  necessity  of  pre- 
venting the  access  of  any  bacteria,  and  especially  patho- 
genic organisms,  after  pasteurization. 

3.  Toxins  and  Decomposition  Products.  —  The 
growth  of  bacteria  in  milk  is  attended  by  the  produc- 
tion of  toxins  and  also  by  the  decomposition  of  some  of 
the  milk  constituents.  The  extent  to  which  these  changes 
occur  will  depend  upon  the  number  of  bacteria  which 
gain  access  to  the  milk  during  the  drawing  of  the  milk 
and  its  subsequent  handling,  the  age  of  the  milk  at  the 
time  of  pasteurization,  and  the  temperature  at  which  it 
has  been  kept  in  the  meantime. 

While  the  true  or  soluble  toxins  (exogenous,  extra- 
cellular) are  destroyed  at  comparatively  low  tempera- 
tures, the  endotoxins  (endogenous,  intracellular)  are 
quite  resistant  to  heat.  Most  of  them  require  a  tempera- 


PASTEURIZATION  211 

ture  of  70°  C.  (158°  F.)  for  their  destruction,  and  some 
will  even  survive  boiling.  Therefore,  there  is  no  cer- 
tainty that  all  toxins  which  may  be  present  in  milk  will 
be  destroyed  even  if  the  milk  is  boiled.  While  there 
is  no  direct  proof  that  milk  containing  toxins  is  injurious 
to  health,  at  the  same  time  we  are  also  without  positive 
knowledge  that  such  milk  is  harmless  ( see  page  45 ) . 

Although  there  is  no  definite  information  regarding 
the  effect  of  heat  upon  the  cleavage  products  resulting 
from  the  breaking  up  of  the  milk  constituents  by  bac- 
teria, we  have  reason  to  believe  that  they  are  not  all 
destroyed  by  heat.  This  is  an  important  point  because 
some  of  these  substances  are  of  a  harmful  character. 

In  the  light  of  our  present  knowledge  regarding  the 
effects  of  pasteurization  upon  toxins  and  cleavage  prod- 
ucts, it  would  seem  advisable  to  limit  the  production  of 
these  substances  as  much  as  possible  by  protecting  the 
milk  from  bacterial  contamination  and  by  promptly 
cooling  it  and  keeping  it  cool  until  it  is  pasteurized.  There 
should  be  a  limit  to  the  number  of  bacteria  which  may 
be  present  in  milk  which  is  to  be  pasteurized,  and  this 
limit  should  be  as  low  as  circumstances  will  permit. 

4.  Nutritive  Properties. — The  statement  is  fre- 
quently made  that  milk  may  be  heated  at  145°  F.  (62.8° 
C.)  for  thirty  minutes  without  affecting  its  nutritive 
properties,  but  this  is  not  confirmed  by  the  experience 
of  Hess,  who  saw  scurvy  develop  in  from  two  to  three 
months  in  nearly  every  one  of  a  group  of  infants  who 
were  being  fed  on  milk  pasteurized  in  that  manner ;  when 
orange  juice  or  potato  water  was  added  to  the  milk  the 
disease  was  cured.  The  observations  of  Plantenga  indi- 
cate that  this  diseased  condition  is  not  due  entirely  to 
the  effect  of  heat  on  the  milk.  He  reports  that  while 


212        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

scurvy  developed  in  23  per  cent,  of  the  children  fed  on 
milk  which  was  pasteurized  24  hours  after  it  was  drawn 
from  the  cow  by  heating  it  at  158°  F.  (70°  C.)  for  30 
minutes,  not  a  single  case  of  the  disease  appeared  in  chil- 
dren receiving  milk  pasteurized  immediately  after  being 
drawn  from  the  cow,  although  it  was  from  the  same  dairy 
and  was  pasteurized  in  the  same  manner.  While  many 
instances  have  been  reported  in  which  infants  have  been 
fed  on  pasteurized  milk  without  harm,  there  appears  to 
be  no  reason  to  doubt  that  milk  loses  some  of  its  antiscor- 
butic properties  in  the  process  of  pasteurization  and  that 
the  age  of  the  milk  is  also  a  factor  in  bringing  about  the 
change. 

The  opinion  prevails  among  medical  practitioners 
that  pasteurized  or  boiled  milk  is  the  cause  of  rickets 
and  malnutrition,  as  well  as  scurvy,  in  children.  The 
development  of  rickets  under  such  circumstances  has 
been  attributed  to  the  conversion  of  the  soluble  phos- 
phates of  lime  and  magnesia  contained  in  milk  into  an 
insoluble  form  by  the  action  of  the  heat.  Malnutrition 
is  thought  to  result  from  pasteurized  or  boiled  milk  being 
less  digestible  than  raw  milk,  a  condition  which  is  be- 
lieved to  be  due  to  the  heat  coagulating  the  proteids  and 
rendering  them  less  susceptible  to  the  action  of  the  diges- 
tive fluids.  According  to  Hupp,  however,  heating  milk 
at  145°  F.  (62.8°  C.)  for  30  minutes  does  not  affect 
the  soluble  phosphates  or  the  albumin.  The  coagulation 
of  the  albumin  begins  at  150°  F.  (65.6°  C.)  and  increases 
with  the  temperature,  but  the  soluble  phosphates  are  not 
affected  by  temperatures  up  to  155°  F.  (68.3°  C.). 
Feeding  experiments  with  animals  to  determine  the  com- 
parative digestibility  of  raw  and  boiled  milk  have  given 
contradictory  results.  While  in  most  instances  no  dif- 


PASTEURIZATION  213 

f erences  were  observed,  in  some  cases  calves  fed  on  boiled 
milk  developed  a  diarrhoea  which  disappeared  when  raw 
milk  was  substituted. 

5.  Ferments  or  Enzymes. — In  the  opinion  of  some 
authorities,  the  ferments  or  enzymes  contained  in  milk 
play  a  very  important  role  in  its  digestion  and  assimila- 
tion.   From  this  standpoint  the  effect  of  heat  on  these 
substances  is  therefore  an  important  consideration  in 
connection  with  the  pasteurization  of  milk.    Most  of  the 
ferments  in  milk  can  withstand  a  temperature  of  from 
60  to  65°  C.  (140  to  149°  F.)  for  some  time,  while  higher 
temperatures  weaken  or  destroy  them. 

6.  Taste. — Milk  does  not  acquire  a  cooked  taste  un- 
less it  is  heated  to  158°  F.  (70°  C.)  or  above. 

7.  Cream  Line. — If  milk  is  exposed  to  a  temperature 
of  70°  C.  (158°  F.)  or  above,  the  cream  will  not  sepa- 
rate.   A  temperature  of  65°  C.  (149°  F.)  for  10  min- 
utes has  no  effect  on  the  separation  of  the  cream,  but 
as  the  time  of  exposure  to  this  temperature  is  increased 
beyond  this  period  the  separation  of  the  cream  is  de- 
layed more  and  more  until  finally,  after  40  minutes  ex- 
posure, it  does  not  separate  at  all.     A  temperature  of 
145°  F.  (62.8°  C.)  for  30  minutes  and  60°  C.  (140°  F.) 
for  as  long  as  50  minutes  has  no  effect  on  the  formation 
of  the  cream  layer.     In  the  commercial  pasteurization 
of  milk,  the  pumping  and  stirring  necessary  to  force 
the  milk  through  the  heater  and  to  bring  it  in  contact 
with  the  heated  surfaces  may  have  the  effect  of  breaking 
up  the  fat  globules  and  thus  interfere  with  cream  sepa- 
rating even  when  the  temperature  has  not  been  suffi- 
ciently high  to  alone  affect  the  cream  line. 

Summarizing  the  facts  which  have  been  definitely 
established  regarding  the  effects  of  pasteurization,  we 


214        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

find  that  a  temperature  of  145°  F.  (62.8°  C.)  for  30  to 
45  minutes,  under  commercial  conditions,  will  destroy 
the  pathogenic  bacteria  which  are  most  likely  to  occur 
in  milk,  with  the  possible  exception  of  tubercle  bacilli, 
and  it  appears  probable  that  this  organism  will  also  be 
destroyed,  although  it  would  be  desirable  to  have  more 
definite  information  on  this  point.  Exposure  to  heat 
to  this  extent,  however,  cannot  be  depended  upon  to 
destroy  all  of  the  toxins  and  the  decomposition  products 
which  may  be  present  in  milk  as  a  result  of  bacterial 
growth,  while,  at  the  same  time,  it  destroys  the  antiscor- 
butic properties  of  milk.  Moreover,  it  is  not  certain 
that  it  does  not  decrease  the  digestibility  of  milk. 

METHODS  OF  PASTEURIZATION 

There  are  three  methods  of  pasteurization: 

1.  The  "flash"  or  continuous  process,  in  which  the 
milk  flows  continuously  and  is  exposed  to  a  heated  sur- 
face for  a  few  seconds. 

2.  The  "holder"  process,  in  which  the  milk  is  heated 
to  a  certain  temperature  and  is  then  held  at  that  tem- 
perature for  a  certain  period. 

3.  Pasteurisation  in  the  Final  Container. — In  this 
method,  the  raw  milk  is  placed  in  the  bottle  in  which  it 
is  to  be  delivered,  the  bottle  is  capped,  and  the  filled 
bottle  is  then  exposed  to  the  desired  degree  of  heat. 

The  "flash"  process  is  less  reliable  than  the  "holder" 
method,  as  not  all  of  the  milk  is  certain  to  be  heated  to 
the  temperature  registered  by  the  thermometer;  some 
may  be  heated  in  excess  of  the  temperature  intended  and 
thus  balance  any  deficiency  of  temperature  in  the  milk 
which  may  not  be  heated  to  the  desired  temperature. 
Furthermore,  a  higher  degree  of  heat  is  required  to  de- 


PASTEURIZATION  215 

stroy  pathogenic  organisms  by  the  "flash"  method  than 
by  the  "holder"  method.  Pasteurization  in  the  final  con- 
tainer is  the  best  method,  because  it  does  not  afford  any 
opportunity  for  the  milk  to  be  reinfected.  But  most 
of  the  apparatus  constructed  to  pasteurize  milk  in  bot- 
tles is  rather  costly  and  it  is  also  more  expensive  to  oper- 
ate than  that  of  the  "  flash  "  or  "  holder  "  variety.  Fur- 
thermore, the  bottles  must  be  tightly  sealed,  and  this 
requires  the  use  of  a  cap  which  is  more  expensive  than 
the  ordinary  kind.  Space  must  be  allowed  for  the  ex- 
pansion of  the  milk  when  it  is  heated,  consequently  the 
bottles  cannot  be  entirely  filled.  Larger  bottles  must 
therefore  be  provided  or  the  consumer  will  receive  short 
measure.  The  vacant  space  permits  the  milk  to  be 
shaken  about,  which  may  disturb  the  cream.  The  cream 
may  also  "butter"  if  the  milk  is  subjected  to  sufficient 
agitation  while  warm. 

The  milk  should  be  cooled  immediately  after  pasteur- 
ization. Sudden  cooling  following  exposure  to  heat 
has  no  effect  in  destroying  bacteria,  as  was  formerly  sup- 
posed, but  prompt  cooling  will  retard  the  development 
of  the  bacteria  or  spores  which  survive  pasteurization. 
The  regulations  of  the  Philadelphia  Board  of  Health 
require  that  the  milk  shall  be  cooled  to  50°  F.  (10°  C.) 
or  below  immediately  after  pasteurization,  held  at  that 
temperature  or  below  while  at  the  pasteurizing  plant, 
and  delivered  to  the  consumer  within  24  hours.  The 
requirements  of  the  New  York  Commission  on  Milk 
Standards  specify  that  the  milk  must  be  cooled  imme- 
diately to  a  temperature  not  exceeding  50°  F.  (10°  C.) 
and  held  at  that  temperature  until  delivered  to  the  con- 
sumer. 

Types  of  Pasteurizers. — Various  types  of  pasteuriz- 


216         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

ing  apparatus  are  in  use.  In  all  of  those  used  in  the 
"flash"  and  "holder"  method,  the  milk  is  exposed  in  some 
way  to  surfaces  heated  by  hot  water  or  steam.  Hot 


M/LK 
OUTLET 


\THERMOMETE? 


STEAM  ANO 
—  WATER 
JACKET 


M/LK 
/A/LET 


STEAM 
/A/LET 


Fio.  24. — A  pasteurizer  of  simple  type  (B.  A.  I.  Giro.  184). 

water  is  best;  it  maintains  the  heating  surfaces  at  a 
more  even  temperature  and  the  milk  is  less  likely  to  be 
scorched  than  when  steam  is  used.  To  meet  the  neces- 
sary requirements,  a  pasteurizer  must  heat  all  of  the 


PASTEURIZATION 


217 


milk  to  the  desired  temperature;  it  must  be  reliable  in 
operation,  and  must  be  convenient  to  clean.  If  a  film  is 
permitted  to  form  on  the  top  of  the  milk,  which  will 
occur  when  milk  is  heated  in  open  vessels,  more  heat 
will  be  required  to  destroy  the  bacteria  contained  in  the 
film  than  in  the  other  parts  of  the  milk. 


WATER 


OUTLET 


M/LK^ 


(0) 


HOT  WATEfr 
/A/LET 


K 


connections  removed 
to  &how  double,  tubes. 


S/DE  W£W 


FIG.  25.— (B.  A.  I.    Circ.  184). 

A  pasteurizer  of  simple  style  is  shown  in  Fig.  24. 
The  milk  enters  through  the  milk  inlet  at  the  bottom 
and  is  forced  against  the  heated  sides  by  the  revolving 
paddle.  Another  type  of  pasteurizer  is  shown  in  Fig. 
25.  This  is  a  system  of  double  tubes  or  pipes.  The 
milk  flows  through  the  inner  tube  in  one  direction  and 


218        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 


the  hot  water  through  the  outer  tube  in  the  opposite 
direction.  The  end  connections  are  removable  to  facili- 
tate cleaning.  Fig.  26  shows  a  "starter  can"  adapted 
to  pasteurize  small  quantities  of  milk.  It  may  also  be 
used  as  a  cooler. 


D 


I  I 

1  r 

it 
u 

|i 

il 

ii 
ii 
u 

f 

.    JL 


1 1 

4-k 


ii 

I 


— +-M/LKTJNK 

XGVOLV/MG 


FIG.  26.— (B.  A.  I.  Circ.  184). 

In  the  "flash"  method  of  pasteurization  the  milk 
passes  from  the  pasteurizer  over  a  cooler.  Sometimes 
a  regenerative  cooler  is  used  in  which  the  milk  to  be 
pasteurized  flows  down  one  side  of  a  corrugated  sheet 
of  metal  and  the  milk  coming  from  the  pasteurizer  flows 
down  the  other  side,  the  cold  milk  thus  absorbing  some 


PASTEURIZATION 


219 


of  the  heat  from  the  hot  milk  before  the  latter  reaches 
the  cooler.  ( See  Fig.  27. )  In  the  "holder"  method,  the 
milk  is  run  from  the  pasteurizer  or  heater  into  the  holder 
or  retarder  to  be  held  at  a  certain  temperature  for  a 
certain  period  of  time.  In  the  holder,  the  milk  stops 


ovnrr  m#  cot& 

A4S7&MKZE9  MS* 

_X 

Fio.  27.— Regenerative  Cooler.     (B.  A.  I.  Circ.  184). 

flowing  and  is  actually  held  for  the  required  time.  On 
the  other  hand,  in  the  retarder  the  flow  continues,  but  is 
slowed  or  retarded  sufficiently  to  hold  the  milk  for  the 
required  period.  The  retarder  is  not  as  reliable  as  the 
holder.  A  simple  and  cheap  holding  tank  is  shown  in 


220        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Fig.  28.  It  was  made  by  dividing  a  receiving  tank  of 
100  gallons  capacity  into  four  compartments  of  25  gal- 
lons capacity  each  and  providing  an  outlet  valve  and  a 
cover  for  each  compartment.  Fig.  29  shows  a  retarder 
of  the  tank  type.  The  milk  from  the  pasteurizer  enters 
at  A  and  is  carried  by  the  pipe  to  the  bottom  of  the 
first  compartment.  When  this  is  filled,  it  overflows  into 
the  trough  C,  whence  the  milk  flows  through  a 
pipe  leading  to  the  bottom  of  the  second  compartment. 
The  other  compartments  are  filled  successively  in  the 


TO  COOLER 

Fio.  28.— A  simple  holding" tank  (B.  A.  I.  Circ.  184). 

same  manner.  When  the  last  compartment  overflows 
the  milk  enters  the  funnel  B  and  passes  to  the  cooler. 
After  all  the  milk  has  come  over  from  the  pasteurizer, 
the  tank  is  emptied  by  removing  the  funnel  B  and  then 
taking  out  the  plugs  from  each  compartment  succes- 
sively. 

A  combined  pasteurizer  and  holder,  which  may  also 
be  used  to  cool  the  milk,  is  shown  in  outline  in  Fig.  30. 
After  the  milk  has  been  heated  to  the  temperature  de- 
sired and  held  for  the  required  time,  it  can  be  cooled 
by  replacing  the  hot  water  with  cold  water  and  then 
with  ice  water  or  brine. 


PASTEURIZATION 


221 


-XJ 


Fio.  29.— Retarder  of  the  tank  type  (B.  A.  I.  Circ.  184). 


FIG.  30.— A  combined  pasteurizer  and  holder  (B.  A.  I.  Giro.  184). 


222        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

There  should  be  an  accurate  thermometer  in  the  out- 
flow pipe  of  the  pasteurizer  and  one  in  the  outflow  pipe 
of  the  holder.  A  reliable  temperature  and  time-record- 
ing apparatus  should  be  connected  with  both  thermom- 
eters and  the  records  should  be  kept  on  file  for  official 
inspection.  These  records  should  show  the  time  of  hold- 
ing as  well  as  the  temperature.  The  efficiency  of  the 
pasteurizing  apparatus  should  also  be  tested  frequently 
by  bacteriological  tests. 

The  commercial  pasteurization  of  milk  should  be 
permitted  only  under  careful  and  competent  official  su- 
pervision. The  inefficiency  of  commercial  pasteurization 
without  proper  supervision  has  been  frequently  demon- 
strated. Two  of  the  worst  milk-borne  epidemics  which 
have  occurred  within  recent  years  (Chicago  1911,  Balti- 
more 1912)  were  due  to  infected  milk  which  was  sup- 
posed to  have  been  pasteurized. 

Biorization. — This  process  consists  in  spraying  milk 
into  a  chamber  in  which  it  is  exposed  to  a  temperature 
of  167°  F.  (75°  C.)  while  under  a  pressure  of  3  to  4 
pounds.  The  apparatus,  which  is  called  a  biorizator,  was 
invented  by  Dr.  Oscar  Lobeck,  in  Germany,  in  1912. 
The  inventor  claims  that  by  this  process  all  of  the  harm- 
ful bacteria  are  destroyed,  while  the  color,  odor,  taste, 
albumen,  ferments,  salts,  and  cream  line  are  not  affected. 

It  has  been  proposed  to  destroy  bacteria  in  milk  by 
subjecting  them  to  the  action  of  ultra-violet  rays,  elec- 
tricity^ and  ozone,  but  the  processes  in  which  these  agents 
are  used  have  all  proved  less  satisfactory  than  pasteuri- 
zation. 


CHAPTER    IX 

METHODS  OF  EXAMINING  MILK 

Milk  may  be  subjected  to  various  methods  of  exami- 
nation for  the  purpose  of  detecting  adulteration  or  dilu- 
tion, the  addition  of  preservatives,  or  the  presence  of 
pathological  products,  and  for  the  determination  of  the 
reaction,  the  bacterial  content,  the  relative  number  of 
leucocytes,  the  quantity  of  sediment  or  dirt,  etc. 

Collecting  Samples. — When  milk  is  permitted  to 
stand  undisturbed,  the  fat  rises  to  the  top  and  the  heavier 
substances  settle  to  the  bottom.  Some  of  the  cells  and 
bacteria  gravitate  to  the  bottom,  but  many  of  them  are 
carried  up  with  the  fat.  The  upper  part  of  the  milk 
contains  more  fat  than  the  lower  even  before  a  cream 
layer  is  visible.  For  these  reasons,  the  milk  in  the  con- 
tainer should  be  thoroughly  mixed  before  a  sample  is 
taken  for  examination.  When  the  milk  is  cold,  consid- 
erable shaking  or  stirring  is  required  to  mix  the  fat 
equally.  In  collecting  samples  of  which  the  specific  grav- 
ity, the  per  cent,  of  fat  and  total  solids  or  the  acidity 
are  to  be  determined,  or  which  are  to  be  tested  for  pre- 
servatives, alkalies,  nitrates  and  nitrites,  etc.,  the  same 
dipper  may  be  used  in  taking  the  different  samples  with- 
out affecting  the  accuracy  of  the  tests.  There  appears 
to  be  some  danger,  however,  of  carrying  typhoid  fever 
and  diphtheria  infection  over  from  one  sample  to  an- 
other, although  we  have  no  proof  of  this  having  actually 
occurred.  The  same  dipper  may  be  used  for  stirring 
and  mixing  the  milk.  But  when  the  bacterial  content 
or  the  ferment  reactions  are  to  be  determined,  each  sam- 

223 


224        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

pie  must  be  collected  in  such  a  manner  as  to  avoid  the 
contamination  of  one  sample  by  another.  The  most  sat- 
isfactory plan  is  to  have  a  sufficient  number  of  sterile 
pipettes  or  aluminum  tubes  of  suitable  size  and  to  use 
a  separate  pipette  or  tube  for  each  sample.  ( See  method 
described  on  page  261.)  The  extension  of  the  custom 
of  delivering  milk  in  bottles  has  greatly  simplified  the 
collection  of  samples  for  laboratory  examination,  espe- 
cially for  the  bacteriological  and  ferment  tests. 

An  instrument  known  as  a  "milk  thief"  is  frequently 
used  to  collect  samples  of  milk  from  vessels  with  straight 
sides,  like  shipping  cans.  It  consists  of  a  metal  tube 
about  23  inches  long  with  a  handle  at  the  upper  end. 
This  tube  is  inserted  slowly  into  the  can  of  milk  in  a 
perpendicular  position  until  the  lower  end  of  the  tube 
rests  on  the  bottom  of  the  can.  The  interior  of  the  tube, 
of  course,  fills  with  milk.  The  opening  at  the  top  is 
closed  tightly  with  the  thumb,  and  the  tube  is  then  lifted 
out  of  the  can,  carrying  with  it  the  column  of  milk  in 
the  interior.  The  milk  thus  withdrawn  may  be  emptied 
into  a  vessel  by  removing  the  thumb  from  the  top  of  the 
tube.  By  this  means,  a  column  of  milk  extending  from 
the  bottom  to  the  top  of  the  fluid  is  obtained,  which  in- 
cludes all  of  the  different  strata  existing  at  various  levels 
in  the  can  and  which  may  therefore  be  regarded  as  a 
representative  sample.  Another  type  of  tube  sampler 
has  a  cap  at  the  lower  end  with  three  openings,  which 
are  closed  when  the  cap  comes  in  contact  with  the  bottom 
of  the  can.  As  the  tube  is  pushed  down  into  the  can, 
the  milk  enters  its  interior  through  these  openings  and 
is  held  there  when  the  cap  is  closed.  The  tube  is  then 
withdrawn  and  the  milk  emptied  into  a  vessel. 

Preserving  Samples. — When  the  samples  are  to  be 


METHODS  OF  EXAMINING  MILK  225 

shipped  some  distance  to  a  laboratory  to  be  tested  for 
specific  gravity,  fat  per  cent.,  and  per  cent,  of  total  solids, 
or  to  be  subjected  to  any  of  the  chemical  tests,  an  anti- 
septic may  be  added  to  preserve  them.  Potassium  dichro- 
mate,  %  gram  to  the  liter  of  milk  (7%  grains  to  the 
quart)  and  formalin,  20  drops  to  the  liter,  are  usually 
used  for  this  purpose.  It  is  better,  however,  to  sterilize 
the  sample  bottle  by  boiling  and  to  close  it  with  a  steril- 
ized stopper.  This  method  must  be  followed  when  bac- 
teriological or  ferment  tests  are  to  be  made,  as  antiseptics 
cannot  be  added  in  such  cases,  and  the  samples  should 
be  packed  in  ice. 

Stable  or  Herd  Samples. — When  a  sample  of  market 
milk  is  tested  and  it  appears  from  the  results  that  the 
milk  has  been  diluted  with  water  or  that  it  has  been 
skimmed  or  diluted  with  skimmed  milk,  a  stable  or  herd 
sample  may  be  taken  at  the  dairy  farm  from  which  the 
suspected  milk  came  and  tested  for  comparison.  On  the 
day  the  herd  sample  is  taken,  the  cows  should  be  fed, 
watered,  and  milked  as  usual  and  by  the  regular  persons ; 
the  two  milkings  should  be  thoroughly  mixed  and  the 
sample  taken  from  the  whole.  If  nitrates  or  nitrites  have 
been  found,  samples  of  the  water  should  also  be  taken 
and  examined.  The  importance  of  the  stable  or  herd 
test  is  variously  regarded.  Some  authorities  do  not  con- 
sider it  of  much  value,  especially  for  small  herds,  because 
of  the  daily  variation  in  the  composition  of  the  milk  of 
the  cow,  particularly  in  the  per  cent,  of  fat.  Others  do 
not  believe  that  accepted  averages  of  the  specific  gravity 
and  composition  of  normal  milk  are  a  safe  basis  for  judg- 
ing milk  in  regard  to  dilution  or  skimming,  and  are  of 
the  opinion  that  a  definite  conclusion  can  only  be  reached 

15 


226        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

after  a  herd  sample  is  tested  and  the  results  compared. 
The  establishment  of  a  legal  standard  for  the  per  cent, 
of  fat  and  total  solids  in  milk  has  made  it  unnecessary  in 
many  states  to  prove  that  milk  has  been  actually  diluted 
or  skimmed.  All  that  is  required  is  to  show  that  the 
fat  and  total  solids  are  below  the  legal  standard;  con- 
sequently the  question  of  taking  a  stable  sample  for  com- 
parison does  not  arise. 

Individual  Samples. — When  a  sample  of  milk  is 
taken  from,  an  individual  cow  for  the  determination  of 
the  specific  gravity  and  the  per  cent,  of  fat  and  total 
solids,  the  milk  should  be  drawn  into  a  pail  in  the  usual 
manner  and  the  sample  taken  from  the  pail  after  the 
milk  has  been  thoroughly  mixed.  If  it  is  desired  to  ascer- 
tain the  average  for  the  day,  which  is  the  usual  method, 
an  equal  quantity  of  milk  is  taken  from  the  morning  and 
evening  milking,  mixed,  and  then  tested.  When  the 
ferment  tests  are  to  be  applied  or  the  number  of  bacteria 
is  to  be  determined,  the  sample  must  be  drawn  with  a 
sterile  pipette  and  placed  in  a  sterile  bottle,  the  contents 
of  the  pail  being  first  thoroughly  mixed.  If  the  milk  is 
to  be  examined  for  pathological  conditions,  a  small  quan- 
tity may  be  milked  from  each  quarter  into  a  sterile  bottle ; 
it  is  best,  however,  to  have  each  quarter  milked  dry  and 
to  collect  a  small  quantity  of  milk  at  the  beginning,  in 
the  middle,  and  at  the  end  of  the  milking. 

Minting  the  Milk  Sample. — Previous  to  removing 
milk  from  the  sample  bottle  for  a  test  in  the  laboratory, 
the  milk  should  be  thoroughly  mixed.  This  may  be 
done  by  inverting  the  bottle  several  times  if  it  is  tightly 
stoppered,  or  by  pouring  the  milk  from  the  bottle  into  a 
beaker  and  back  again  several  times.  No  cream  should 


METHODS  OF  EXAMINING  MILK  227 

be  permitted  to  adhere  to  the  stopper  or  to  the  sides  of 
the  bottle.  If  the  bottle  has  been  standing  for  several 
hours  and  the  milk  has  been  thoroughly  chilled,  it  may 
be  necessary  to  warm  the  sample  in  order  to  avoid  this. 

Color,  Consistency,  Odor,  and  Taste. — As  a  prelim- 
inary examination,  the  color,  consistency,  odor,  and  taste 
of  the  milk  should  be  observed.  The  senses  of  smell  and 
taste  soon  tire,  however,  and  it  is  therefore  not  possible 
to  properly  examine  many  samples  consecutively. 

A  bluish  tinge  may  indicate  a  low  per  cent,  of  fat, 
skimming,  or  watering,  but  it  must  be  remembered  that 
any  milk  will  have  a  bluish  tinge  if  in  a  thin  layer.  A 
reddish  tinge  is  sometimes  observed  in  milk  from  an 
udder  affected  with  mastitis.  Various  other  changes  in 
color  may  occur  as  the  result  of  bacterial  action  (see 
page  71). 

Thin  or  watery  milk  is  an  indication  of  dilution  with 
water  or  of  skimming.  Flakes  or  curds  are  present  in 
milk  from  an  udder  affected  with  mastitis.  Other  changes 
in  consistency  are  caused  by  bacteria  (see  pages  67  and 
69). 

Abnormal  odors  may  be  absorbed  from  the  atmos- 
phere or  may  be  caused  by  bacteria  (see  pages  29,  30, 
67  and  71). 

A  salty  or  bitter  taste  is  present  in  mastitis  and  indi- 
gestion, also  near  the  end  of  lactation  and  just  before 
parturition.  A  bitter,  metallic  taste  may  be  due  to  rusted 
milk  vessels.  Milk  may  also  have  an  abnormal  taste 
as  a  result  of  the  growth  of  certain  bacteria,  the  absorp- 
tion of  gases,  and  from  other  causes  ( see  pages  28  to  30 
and  66  to  71).  Heating  milk  will  make  an  abnormal 
odor  more  pronounced. 


228         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 
DETERMINATION  OF  SPECIFIC  GRAVITY 

The  specific  gravity  of  milk  is  determined  by  means 
of  Quevenne3  s  lactometer  ( Fig.  31 )  or  modifications  of 
this  apparatus. 

After  being  thoroughly  mixed,  some  of  the  milk  to 
be  tested  is  poured  into  a  high  glass  cylinder  and  the 
lactometer  is  slowly  and  carefully  lowered 
into  the  fluid  until  it  floats.  Care  should 
be  taken  not  to  mix  air  with  the  milk. 
This  can  be  avoided  by  pouring  the  milk 
against  the  side  of  the  vessel.  The  lacto- 
meter must  not  be  permitted  to  touch 
the  side  of  the  cylinder.  When  the 
lactometer  has  become  stationary,  the 
specific  gravity  is  indicated  by  the 
figures  on  the  scale  in  the  stem  of  the 
lactometer.  The  reading  is  taken  from 
the  line  in  the  scale  which  is  on  a  level 
with  the  surface  of  the  milk.  The  stem 
of  the  lactometer  draws  the  milk  up 
around  it,  forming  a  slight  meniscus 
which  obscures  the  line  at  the  surface  of 
the  milk.  The  reading  should  not  be 
taken  from  the  top  of  this  meniscus,  but 
at  the  surface  of  the  milk,  the  depth  of 
the  meniscus  being  estimated.  The 

Fio.  31. — Quevenne 'B 

lactometer.  figures  on  the  lactometer  scale  do  not  ex- 
press the  specific  gravity  but  Quevenne  degrees.  By 
dividing  Quevenne  degrees  by  1000  and  adding  1,  the 
specific  gravity  is  obtained. 

The  temperature  of  the  milk  should  be  15°  C.  (60° 
F. )  when  the  specific  gravity  is  taken,  and  the  tempera- 
ture should  be  taken  with  an  accurate  thermometer  after 


METHODS  OF  EXAMINING  MILK  229 

the  milk  has  been  placed  in  the  glass  cylinder  and  the 
lactometer  introduced.  The  lactometer  reading  and  the 
temperature  should  be  taken  as  nearly  as  possible  at 
the  same  time.  If  the  temperature  of  the  milk  is  not 
exactly  15°  C.  (60°  F.),  then  the  specific  gravity  at  this 
temperature  must  be  calculated  from  the  lactometer  and 
thermometer  reading,  because  this  is  the  standard  tem- 
perature. Adding  to  the  specific  gravity  0.0002  for  each 
degree  Centigrade  above  15  or  0.0001  for  each  degree 
Fahrenheit  above  60,  and  subtracting  the  same  numbers 
for  each  degree  below  the  standard  temperature,  will 
give  the  approximate  specific  gravity  at  the  standard 
temperature ;  but  more  accurate  results  will  be  obtained 
by  using  the  tables  on  pages  230  and  231.  If,  for  exam- 
ple, the  lactometer  reading  is  28  and  the  temperature  is 
17°  C.,  locate  1.028  in  the  column  at  the  extreme  left  and 
follow  this  line  to  the  right  to  the  column  headed  17°  C. ; 
the  figures  at  this  point,  28.4,  represent  the  lactometer 
reading  at  15°  C.  To  obtain  exact  results,  the  specific 
gravity  should  be  taken  with  the  milk  at  15°  C.,  because 
lactometers  are  calibrated  for  this  temperature.  After 
the  specific  gravity  is  taken  the  lactometer  should  be 
rinsed  with  water  and  wiped  dry. 

The  specific  gravity  of  milk  may  also  be  determined 
by  means  of  the  Westphal  balance  (Fig.  32).  This  in- 
strument consists  of  a  pivoted  beam  with  a  float  hanging 
from  one  end.  The  milk  to  be  tested  is  placed  in  a  glass 
cylinder  and  the  float  is  let  down  into  the  milk.  The 
weights  on  the  beam  are  then  moved  until  equilibrium 
is  established,  and  the  specific  gravity  is  indicated  by  the 
position  of  the  weights. 

The  specific  gravity  of  normal  market  milk  ranges 
from  1.028  to  1.034,  the  average  being  1.032.  Skimming 


230         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 


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METHODS  OF  EXAMINING  MILK 


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232        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

off  the  cream  or  adding  skimmed  milk  increases  the  spe- 
cific gravity,  while  the  addition  of  water  decreases  it.  It 
is  not  possible  to  detect  these  forms  of  adulteration  from 
the  change  in  specific  gravity  alone,  on  account  of  the 
wide  range  in  the  specific  gravity  of  normal  milk,  but 
when  considered  in  connection  with  the  per  cent,  of  fat 
and  solids  not  fat  the  specific  gravity  is  of  great  assist- 
ance. The  specific  gravity  of  skimmed  milk  may  be 
lowered  to  normal  by  the  addition  of  a  suitable  quantity 
of  water.  When  this  is  suspected, 
the  determination  of  the  specific 
gravity  of  the  dry  matter  or  solids 
and  the  per  cent,  of  fat  in  the  total 
solids  will  throw  further  light  on 
the  subject.  The  test  for  nitrates 
and  nitrites  will  assist  in  discover- 
ing the  addition  of  water  (see  page 
247).  The  refraction  number  of 
the  milk  serum  is  also  of  value  in 
this  connection  (see  page  250). 

It  is  necessary  to  refer  to  the 
New  York  Board  of  Health  lac- 
tometer because  it  is  still  used  to  some  extent  in 
the  East,  although  it  is  constructed  on  the  incorrect 
theory  that  1.029  is  the  lowest  specific  gravity  of  pure 
milk.  Its  scale  is  divided  into  120  divisions.  One  hun- 
dred corresponds  to  29  Quevenne  degrees,  or  a  specific 
gravity  of  1.029.  Milk  testing  90  on  this  scale  is  sup- 
posed to  be  90  per  cent,  pure,  i.e.,  10  per  cent,  of  water 
is  supposed  to  have  been  added,  which,  of  course,  is 
not  always  true.  Readings  on  this  scale  may  be  con- 
verted into  Quevenne  degrees  by  multiplying  by  0.29 
or  the  following  table  may  be  used: 


Fio.  32.— Westphal  balance. 
(From  Chemical  Testing  of  Milk 
and  Cream,  by  R.  H.  Shaw, 
U.  8.  Dept.  of  Agriculture.) 


METHODS  OF  EXAMINING  MILK 


233 


Board  of 
health  degrees 

Quevenne 
scale 

Board  of 
health  degrees 

Quevenne 
scale 

Board  of 
health  degrees 

Quevenne 
scale 

61 

17-7 

81 

23-5 

101 

29-3 

62 

18-0 

82 

23-8 

102 

29-6 

63 

18-3 

83 

24-1 

103 

29-9 

64 

18-6 

84 

24-4 

104 

30-2 

65 

18-8 

85 

24-6 

105 

30-5 

66 

19-1 

86 

24-9 

106 

30-7 

67 

19-4 

87 

25-2 

107 

31-0 

68 

19-7 

88 

25-5 

108 

31-3 

69 

20-0 

89 

25-8 

109 

31-6 

70 

20-3 

90 

26-1 

110 

31-9 

71 

20-6 

91 

26-4 

111 

32-2 

72 

20-9 

92 

26-7 

112 

32-5 

73 

21-2 

93 

27-0 

113 

82-8 

74 

21-5 

94 

27-3 

114 

33-1 

75 

21-7 

95 

27-6 

115 

33-4 

76 

22-0 

96 

27-8 

116 

33-6 

77 

22-3 

97 

28-1 

117 

83-9 

78 

22-6 

98 

28-4 

118 

34-2 

70 

22-9 

99 

28-7 

119 

34-5 

80 

23-2 

100 

29-0 

120 

34-8 

DETERMINATION  OF  THE  PER  CENT.  OF  FAT 

Babcock  Test.— The  method  devised  by  Dr.  S.  M. 
Babcock  is  the  one  most  commonly  used  in  the  United 
States  for  determining  the  per  cent,  of  fat  in  milk  and 
other  dairy  products.  The  apparatus  required  consists 
of  a  bottle  of  about  50  c.c.  capacity  with  a  long  neck 
containing  graduations  from  which  the  per  cent,  of  fat 
can  be  read  off,  a  pipette  holding  17.6  c.c.,  and  a  small 
measuring  cylinder  graduated  to  measure  17.5  c.c.  A 
centrifuge  is  also  necessary.  The  graduations  on  the 
neck  of  the  old  type  of  bottle  extend  from  0  to  10  per 
cent.,  with  subdivisions  of  0.2  per  cent.,  but  on  the  more 
recent  type  the  scale  is  divided  into  tenths  and  extends 
from  0  to  8  per  cent.  Only  glassware  should  be  used 
which  has  been  tested  and  approved  by  the  United  States 
Bureau  of  Standards.  Commercial  sulphuric  acid  with 
a  specific  gravity  of  1.82  to  1.83  at  60°  F.  is  used  in 


234        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

making  the  test.  The  acid  dissolves  the  solids  not  fat 
and  liberates  the  fat  from  its  emulsion,  generates  heat 
which  causes  the  fat  globules  to  run  together,  and  in- 
creases the  specific  gravity  of  the  serum.  The  test  is 
made  as  follows:  The  temperature  of  the  milk  should 


/\ 


Fio.33. — Modern  type  of  Babcock  milk-  Fra.  34. — Pipette  used  in  Babcock 

testing  bottle  conforming  to  the  require-  testfor  measuring  milk.  'From  Chem- 

ments  of  the  U.  S.  Bureau  of  Standards.  ical  Testing  of  Milk  and  Cream,  by 

(From   Chemical    Testing  of    Milk    and  R.  H.  Shaw,  U.  S.  Dept.  of  Agriculture.) 
Cream,  by  R.  H.  Shaw,  U.  S.  Dept.  of  Ag- 
riculture.) 

be  between  60°  and  70°  F.  After  the  milk  has  been 
thoroughly  mixed,  the  tip  of  the  pipette  is  inserted  just 
beneath  the  surface  and  filled  to  the  17.6  c.c.  mark. 
The  pipette  is  then  inserted  obliquely  into  the  mouth  of 
the  bottle  and  the  milk  permitted  to  run  slowly  down 
the  inside  of  the  neck.  When  the  milk  ceases  flowing, 
the  pipette  is  blown  into  to  force  out  any  residue.  To 


METHODS  OF  EXAMINING  MILK  235 

obtain  accurate  results,  every  particle  of  milk  must  be 

delivered  into  the  bottle.     The  measuring  cylinder  is 

filled  to  the  17.5  c.c.  mark  with  sulphuric  acid;  then, 

with  the  bottle  held  by  the  neck  in  an  oblique  position, 

the  acid  is  poured  slowly  down  the  side,  the  bottle  being 

rotated  slowly  so  that  any  milk  in  the  neck  will  be  washed 

down.    The  acid  and  milk  are  then  mixed  by  grasping 

the  bottle  by  the  neck  and  gently  whirling  it,  first  to  the 

right  and  then  to  the  left,  or  by  holding  the  bottle  by 

the  neck  in  an  inclined  position  with  the  edge  of  the  bot- 

tom resting  on  a  table  and  rotating  it, 

first  in  one  direction  and  then  in  the 

other.     When   mixing   is   once   com- 

menced  it  must   be   continued   until 

solution    is    complete.    The    solution 

should  finally  be  of  a  dark  brown  color, 

The  bottle  is  placed  in  a  centrifuge 

and  whirled  for  five  minutes  at  a  speed 

of  800  to  1200  revolutions  per  minute.  ^  —  ^ 

Fio.  35.—  Cylinder  used 

Hot  water   at   a  temperature  above 


175 

CO 


120°  R  (49°  C.)  is  then  added  until 
the  bottle  is  filled  to  the  bottom  of  the  u-s'Dept'  °f  AgricuUure0 
neck  and  the  bottle  is  replaced  in  the  centrifuge  and 
whirled  for  two  minutes.  Hot  water  is  again  added  until 
the  fluid  in  the  bottle  is  raised  to  a  point  near  the  top 
of  the  graduated  scale,  the  water  being  dropped  directly 
into  the  fluid,  not  run  down  the  side,  in  order  to  remove 
any  flocculent  material  which  may  be  entangled  in  the 
fat  at  the  top.  The  bottle  is  then  whirled  another  min- 
ute. After  the  whirling  is  completed,  the  fat  should  be 
collected  at  the  top  of  the  fluid  in  the  bottle  in  a  column 
of  clear,  yellowish  liquid,  with  a  nearly  colorless  fluid 
below  it.  The  fat  column  should  have  a  well-defined 


236        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

meniscus  at  the  top  and  bottom,  and  the  reading  should 
be  made  from  the  bottom  of  the  lower  meniscus  to  the 
top  of  the  upper  one.  A  pair  of  calipers  will  be  found 
convenient  for  measuring  the  fat  column.  The  tem- 
perature of  the  contents  of  the  bottle  should  be  between 
130°  and  140°  F.  (54°  to  60°  C.)  when  the  reading  is 
taken.  Foam  on  the  top  of  the  fat  column  is  caused  by 
using  hard  water.  Dark  colored  particles  in  the  fat 
column  may  be  due  to  several  causes:  acid  too  concen- 
trated, too  much  acid,  milk  too  warm  when  acid  was 
added,  allowing  acid  to  mix  with  milk  when  placing  it 
in  the  bottle,  allowing  the  bottle  to  stand  too  long  before 
mixing  the  acid  and  milk,  and  interrupting  the  mixing 
before  the  solution  was  complete.  White  particles  in 
the  fat  column  may  result  from  acid  which  is  too  weak, 
too  little  acid,  acid  or  milk  being  too  cold,  and  insuffi- 
cient mixing.  Immediately  after  the  reading  is  taken 
the  bottle  should  be  emptied,  rinsed  out  twice  with  boil- 
ing water  and  placed  in  a  rack  to  drain.  Now  and  then 
the  bottles  should  be  washed  in  a  solution  of  soap  powder 
or  in  a  dilute  solution  of  lye. 

The  Babcock  test  for  fat  in  cream  is  made  in  very 
much  the  same  manner  as  for  milk,  except  that  a  bottle 
with  a  longer  neck  and  more  extensive  graduations  is 
used  and  the  cream  is  weighed  instead  of  measured. 
There  are  two  sizes  of  bottles,  one  for  9  grammes  and 
the  other  for  18  grammes  of  cream.  The  test  bottle  is 
placed  on  the  scales  and  the  cream  is  introduced  into  the 
bottle  with  a  pipette.  Sufficient  sulphuric  acid  is  added 
to  give  the  mixture  the  color  of  coffee;  the  quantity 
required  will  vary  with  the  per  cent,  of  fat  in  the  cream. 
The  bottle  is  then  whirled  in  the  centrifuge  and  water 
added  exactly  as  in  testing  milk.  On  being  finally  re- 


METHODS  OF  EXAMINING  MILK 


237 


moved  from  the  centrifuge,  the  bottle  is  placed  in  water 
at  a  temperature  of  135°  to  140°  F.  (57°  to  60°  C.) 
and  submerged  to  a  point  above  the  fat  column  for  15 
minutes,  after  which  the  per  cent,  of  fat  is  read  off  from 
the  scale.  The  reading  is  taken  from  the  bottom  of  the 
lower  meniscus  to  the  bottom  of  the  upper  one.  It  is 
recommended  that  the  upper  meniscus  be  destroyed  by 
dropping  a  few  drops  of  glymol 
(liquid  petrolatum,  white  min- 
eral oil)  into  the  test  bottle  and 
the  reading  taken  from  the  bot- 
tom of  the  lower  meniscus  to 
the  line  between  the  glymol  and 
the  fat. 

Gerber  Test.— (Fig.  36.) 
This  test  is  used  almost  exclu- 
sively in  Europe  and  to  some  ex- 
tent in  this  country.  The  prin- 
ciple is  the  same  as  in  the  Bab- 
cock  test,  except  that  the  fat  is 
not  only  liberated  from  its  emul- 
sion by  sulphuric  acid  but  is 
also  dissolved  in  amyl  alcohol. 
The  apparatus  required  con- 

x  A  Fio.  36.— Bottle  and  pipettes  used  in 

sists  of  a  special  type  of  bottle  Gerber  test. 

(G)  known  as  an  acido-butyrometer,  which  has  a  long 
neck  containing  a  scale  graduated  in  tenths,  each  division 
representing  0.1  per  cent,  of  fat,  and  an  opening  in  the 
bottom  which  may  be  closed  with  a  rubber  stopper ;  also 
three  pipettes:  1  of  11  c.c.  capacity  to  measure  the  milk 
(K),  an  acid  pipette  holding  10  c.c.  (H),  and  a  1  c.c. 
pipette  for  the  amyl  alcohol  (I).  The  chemicals  used 
are  commercial  sulphuric  acid  of  a  specific  gravity  of 


238        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

1.825  at  15°  C.  and  amyl  alcohol.  The  test  is  made  as 
follows :  The  milk  and  the  chemicals  should  be  at  a  tem- 
perature of  15°  C. ;  10  c.c.  of  sulphuric  acid  are  measured 
with  the  acid  pipette  and  placed  in  the  bottle.  The  point 
of  the  pipette  should  be  passed  obliquely  through  the 
opening  of  the  bottle  until  it  comes  in  contact  with  the 
side  of  the  bottle,  when  the  acid  is  allowed  to  flow  slowly 
out.  Care  should  be  taken  that  no  acid  is  deposited  in 
the  spiral  grooves  on  the  inner  side  of  the  opening.  After 
thoroughly  mixing  the  milk,  11  c.c.  are  drawn  up  into 
the  proper  pipette  and  placed  in  the  bottle  with  the 
same  precautions,  the  milk  being  permitted  to  flow 
slowly  down  the  side  of  the  bottle  so  that  it  will  not  mix 
with  the  acid.  Then  1  c.c.  of  amyl  alcohol  is  placed  in 
the  bottle  in  the  same  manner  with  the  alcohol  pipette. 
The  three  fluids  should  be  arranged  in  three  distinct 
layers.  The  bottle  is  closed  with  the  rubber  stopper  and 
the  fluids  are  mixed  by  slowly  raising  first  one  end  of  the 
bottle  and  then  the  other,  permitting  the  fluid  to  flow  in 
and  out  of  the  neck.  This  is  continued  until  a  perfect 
solution  is  obtained.  The  rubber  stopper  should  be 
forced  in  sufficiently  to  raise  the  fluid  to  the  zero  mark 
on  the  scale  in  the  neck  and  it  should  be  held  in  place 
with  the  thumb  while  the  bottle  is  being  shaken.  This 
latter  precaution  is  taken  to  prevent  the  stopper  from 
coming  out,  although  this  is  not  likely  to  occur  if  it  is 
properly  inserted.  The  bottle  should  be  placed  in  a 
water  bath  at  a  temperature  of  60°  to  65°  C.  (140°  to 
150°  F.),  with  the  stopper  downward  and  the  water 
covering  the  entire  bottle,  until  it  is  centrifugalized.  This 
will  not  be  necessary,  however,  when  only  one  or  two 
samples  are  being  tested.  If  a  hand  centrifuge  is  used 
the  whirling  must  be  continued  10  minutes,  but  with  a 


METHODS  OF  EXAMINING  MILK 


239 


power  machine  making  800  to  1000  revolutions  per  min- 
ute 3  to  4  minutes  is  sufficient.  When  the  bottles  are 
removed  from  the  centrifuge  they  should  be  submerged 
in  an  upright  position,  with  the  stopper  downward,  in 
a  water  bath  at  60°  C.  (140  °  F.)  until  the  reading  is 
taken,  unless  the  samples  are  so  few  that  they  can  all  be 
read  in  a  few  seconds.  The  fat  collects  in 
a  clear,  yellow  column  at  the  top  of  the 
fluid  in  the  neck.  The  stopper  is  turned 
sufficiently  to  bring  the  lower  border  of 
the  fat  column  on  a  level  with  one  of  the 
main  divisions  of  the  scale  and  the  per 
cent,  of  fat  is  then  read  off.  The  read- 
ing is  taken  from  the  bottom  of  the  fat 
column  to  the  lower  border  of  the  menis- 
cus at  the  top.  After  the  reading  is  taken 
the  bottle  should  be  emptied  at  once  and 
cleaned  as  directed  for  the  Babcock  bottle. 

A  special  bottle  is  made  for  testing 
cream.  The  cream  placed  in  the  bottle  is 
weighed;  otherwise  the  per  cent,  of  fat  in 
cream  is  determined  in  the  same  manner 
as  that  in  milk. 

Lactoscope  Test. — It  was  proposed 
some  time  ago  to  determine  the  per  cent. 


FIG.  37. — Feser's 


of  fat  in  milk  by  measuring  its  transpar-  iactoscope. 
ency.  Several  forms  of  apparatus  have  been  devised  for 
this  purpose,  the  simplest  being  Feser's  Iactoscope  (Fig. 
37).  This  is  a  glass  tube,  contracted  towards  the  bot- 
tom. A  vertical  white-glass  column,  which  is  encircled 
by  six  blaek  horizontal  lines,  projects  upward  into  the 
contracted  part.  On  the  surface  of  the  upper  part  of  the 
tube  there  is  a  graduated  scale  with  a  column  of  figures 


240        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

at  either  side,  one  column  representing  the  capacity  in 
cubic  centimetres  and  the  other  standing  for  per  cent,  of 
fat.  The  test  is  made  as  follows :  4  c.c.  of  the  milk  to  be 
tested  are  placed  in  the  glass  tube  and  water  is  added  up 
to  the  line  marked  40.  The  two  fluids  are  mixed  and  the 
apparatus  is  then  held  at  arm's  length  with  the  back  of 
the  examiner  to  the  light.  If  the  black  lines  on  the  ver- 
tical column  can  be  distinguished,  then  the  figure  in  the 
per  cent,  column  opposite  the  line  which  is  on  a  level  with 
the  top  of  the  fluid  is  supposed  to  represent  the  per  cent, 
of  fat.  If  the  black  lines  are  not  visible,  then  water  is 
added  until  the  fluid  is  on  a  level  with  the  next  line  on  the 
scale  and  the  fluid  is  mixed  by  shaking;  this  is  repeated 
until  the  black  lines  can  be  seen,  when  the  per  cent,  of  fat 
is  read  off.  This  test  is  inaccurate  because  the  degree  of 
opacity  of  milk  is  not  dependent  entirely  upon  the  quan- 
tity of  fat  but  is  also  influenced  by  the  size  of  the  fat 
globules  and  by  the  calcium  caseinate  (see  page  28). 
An  error  of  0.5  to  1  per  cent,  in  either  direction  may 
occur  in  the  examination  of  whole  milk  and  the  fat  per 
cent,  indicated  for  skim  milk  is  usually  too  high. 

DETERMINATION  OF  TOTAL  SOLIDS 

Gravimetric  Method. — The  apparatus  required  in- 
cludes evaporating  dishes,  an  accurate  analytical  balance 
with  weights,  a  pipette,  a  water  bath,  a  hot-water  oven, 
and  a  desiccator.  Platinum  dishes  are  the  most  desirable, 
but  porcelain  and  silica  dishes  are  satisfactory  and  much 
cheaper;  they  should  have  a  diameter  of  not  less  than  5 
centimetres. 

The  dishes  are  cleaned  and  dried,  placed  in  the  hot- 


METHODS  OF  EXAMINING  MILK  241 

water  oven  for  a  half  hour,  removed  to  the  desiccator 
until  cool  and  then  weighed.  After  they  are  placed  in 
the  oven  they  should  be  handled  with  tongs  or  forceps 
and  should  not  be  touched  with  the  fingers.  As  each 
dish  is  weighed  the  weight  is  recorded.  The  milk  sample 
is  mixed  thoroughly  and  some  of  the  milk  (3  to  5  c.c.)  is 
transferred  to  the  dish,  which  is  again  weighed,  the 
weight  being  recorded.  The  dish  is  placed  on  a  water 
bath  where  it  remains  until  the  milk  is  evaporated  to 
dryness.  It  is  then  removed  to  the  desiccator  and  when 
cool  it  is  weighed.  Following  this  it  is  placed  in  the 
hot-water  oven  for  30  minutes,  after  which  it  is  again 
cooled  in  the  desiccator  and  weighed.  If  the  two  weigh- 
ings agree,  or  are  within  0.2  milligramme  of  each  other, 
the  water  has  all  been  driven  off .  If  the  weighings  do 
not  agree  to  this  extent,  the  dish  must  be  returned  to 
the  hot-water  oven  for  another  period,  then  placed  in  the 
desiccator  until  cool  and  again  weighed,  and  this  must 
be  continued  until  the  weight  is  constant,  or  within  0.2 
milligramme  of  being  the  same.  The  last  weight  minus 
the  weight  of  the  dish  represents  the  weight  of  the  dry 
matter  or  total  solids  in  the  charge  of  milk.  Multiplying 
the  weight  of  the  dry  matter  by  100  and  dividing  by  the 
weight  of  the  charge  will  give  the  per  cent,  of  dry  matter 
in  milk.  The  per  cent,  of  ash  may  be  determined  by 
heating  the  dry  matter  until  the  ash  is  free  from  carbon, 
placing  the  dish  in  the  desiccator  until  cool,  weighing, 
subtracting  the  weight  of  the  dish,  multiplying  the  re- 
mainder by  100  and  dividing  by  the  weight  of  the  charge. 
By  Calculation. — There  are  several  formulas  for 
calculating  the  total  solids  and  solids  not  fat  from  the 
specific  gravity  and  per  cent,  of  fat.  Of  these  Babcock's 

16 


242         PRINCIPLES  AND  PRACTICE  OF  MILK   HYGIENE 

formula  gives  the  most  accurate  results  when  compared 
with  gravimetric  determinations.  This  formula  is  as 
follows  : 


Per  cent,  solids  not  ^=-1     X  (100  -f)  2.5 
S  =  specific  gravity;  f  =per  cent,  of  fat. 

The  results  obtained  with  this  formula  will  not  differ 
more  than  0.25  to  0.5  per  cent,  from  those  obtained  by 
the  gravimetric  method.  A  table  prepared  by  Shaw  and 
Eckles,  which  renders  it  unnecessary  to  make  the  cal- 
culation for  each  sample,  will  be  found  on  pages  243  to 
245.  The  Babcock  formula  determines  the  per  cent,  of 
solids  not  fat,  but  this  table  gives  the  per  cent,  of  total 
solids  ;  it  is  a  modification  of  one  prepared  by  Dr.  Bab- 
cock.  In  the  table  the  per  cent,  of  total  solids  in  any 
given  sample  will  be  found  at  the  intersection  of  the 
column  headed  by  the  number  representing  the  lactom- 
eter reading  (Quevenne  degrees)  and  the  line  corre- 
sponding to  the  fat  per  cent.,  provided  the  lactometer 
reading  is  a  whole  number.  If  the  lactometer  reading  is 
not  a  whole  number  then  the  per  cent,  of  total  solids  is 
found  for  the  whole  number  and  to  this  is  added  the 
fraction  found  opposite  the  decimal  in  the  table  for 
"  proportional  parts."  Take,  for  example,  a  sample  of 
milk  with  a  lactometer  reading  of  33.5  and  a  fat  per 
cent,  of  3.5.  At  the  point  where  the  column  headed  33 
and  the  line  marked  3.5  per  cent,  fat  intersect  are  the 
figures  12.46.  In  the  table  for  "  proportional  parts," 
opposite  the  decimal  .5  is  the  fraction  .13.  This  added 
to  12.46  equals  12.59,  which  represents  the  per  cent,  of 
total  solids. 


TABLE  FOB    DETERMINING   TOTAL  SOLIDS  IN  MILK  FROM  ANY  GIVEN   SPECIFIC 
GRAVITY  AND  PERCENTAGE  OF  FAT 


Per- 

cent- 

Lactometer  reading  at  60°  F.  (Quevenne  degrees) 

age  of 
fat 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

total 

total 

total 

total 

total 

total 

total 

total 

total 

total 

total 

solids 

solids 

solids 

solids 

solids 

solid* 

solids 

solids 

solids 

solids 

solids 

2.00 

8.90 

9.15 

9.40 

9.65 

9.90 

10.15 

10.40 

10.66 

10.91 

11.16 

11.41 

2.05 

8.96 

9.21 

9.46 

9.71 

9.96 

10.21 

10.46 

10.72 

10.97 

11.22 

11.47 

2.10 

9.02 

9.27 

9.52 

9.77 

10.02 

10.27 

10.52 

10.78 

11.03 

11.28 

11.53 

2.15 

9.08 

9.33 

9.58 

9.83 

10.08 

10.33 

10.58 

10.84 

11.09 

11.34 

11.59 

2.20 

9.14 

9.39 

9.64 

9.89 

10.14 

10.39 

10.64 

10.90 

11.15 

11.40 

11.65 

2.25 

9.20 

9.45 

9.70 

9.95 

10.20 

10.45 

10.70 

10.96 

11.21 

11.46 

11.71 

2.30 

9.26 

9.51 

9.76 

10.01 

10.26 

10.51 

10.76 

11.02 

11.27 

11.52 

11.77 

2.35 

9.32 

9.57 

9.82 

10.07 

10.32 

10.57 

10.82 

11.08 

11.33 

11.58 

11.83 

2.40 

9.38 

9.63 

9.88 

10.13 

10.38 

10.63 

10.88 

11.14 

11.39 

11.64 

11.89 

2.45 

9.44 

9.69 

9.94 

10.19 

10.44 

10.69 

10.94 

11.20 

11.45 

11.70 

11.95 

2.50 

9.50 

9.75 

10.00 

10.25 

10.50 

10.75 

11.00 

11.26 

11.51 

11.76 

12.01 

2.55 

9.56 

9.81 

10.06 

10.31 

10.56 

10.81 

11.06 

11.32 

11.57 

11.82 

12.07 

2.60 

9.62 

9.87 

10.12 

10.37 

10.62 

10.87 

11.12 

11.38 

11.63 

11.88 

12.13 

2.65 

968 

9.93 

10.18 

10.43 

10.68 

10.93 

11.18 

11.44 

11.69 

11.94 

1?  19 

2.70 

9.74 

9.99 

10.24 

10.49 

10.74 

10.99 

11.24 

11.50 

11.75 

12.00 

12.25 

2.75 

9.80 

10.05 

10.30 

10.55 

10.80 

11.05 

11.31 

11.56 

11.81 

12.06 

12.31 

2.80 

9.86 

10.11 

10.36 

10.61 

10.86 

11.11 

11.37 

11.62 

11.87 

12.12 

12.37 

2.85 

9.92 

10.17 

10.42 

10.67 

10.92 

11.17 

11.43 

11.68 

11.93 

12.18 

12.43 

2.90 

9.98 

10.23 

10.48 

10.73 

10.98 

11.23 

11.49 

11.74 

11.99 

12.24 

12.49 

2.95 

10.04 

10.29 

10.54 

10.79 

11.04 

11.30 

11.55 

11.80 

12.05 

12.30 

12.55 

3.00 

10.10 

10.35 

10.60 

10.85 

11.10 

11.36 

11.61 

11.86 

12.11 

12.36 

12.61 

3.05 

10.16 

10.41 

10.66 

10.91 

11.17 

11.42 

11.67 

11.92 

12.17 

12.42 

12.68 

3.10 

10.22 

10.47 

10.72 

10.97 

11.23 

11.48 

11.73 

11.98 

12.23 

12.48 

12.74 

3.15 

10.28 

10.53 

10.78 

11.03 

11.29 

11.54 

11.79 

12.04 

12.29 

12.55 

12.80 

3.20 

10.34 

10.59 

10.84 

11.09 

11.35 

11.60 

11.85 

12.10 

12.35 

12.61 

12.86 

3.25 

10.40 

10.65 

10.90 

11.16 

11.41 

11.66 

11.91 

12.16 

12.42 

12.67 

12.92 

3.30 

10.46 

10.71 

10.96 

11.22 

11.47 

11.72 

11.97 

12.22 

12.48 

12.73 

12.98 

3.35 

10.52 

10.77 

11.03 

11.28 

11.53 

11.78 

12.03 

12.28 

12.54 

12.79 

13.04 

3.40 

10.58 

10.83 

11.09 

11.34 

11.59 

11.84 

12.09 

12.34 

12.60 

12.85 

13.10 

3.45 

10.64 

10.89 

11.15 

11.40 

11.65 

11.90 

12.15 

12.40 

12.66 

12.91 

13.16 

3.50 

10.70 

10.95 

11.21 

11.46 

11.71 

11.96 

12.21 

12.46 

12.72 

12.97 

13.22 

3.55 

10.76 

11.02 

11.27 

11.52 

11.77 

12.02 

12.27 

12.52 

12.78 

13.03 

13.28 

3.60 

10.82 

11.08 

11.33 

11.58 

11.83 

12.08 

12.33 

12.58 

12.84 

13.09 

13.34 

3.65 

10.88 

11.14 

11.39 

11.64 

11.89 

12.14 

12.39 

12.64 

12.90 

13.15 

13.40 

3.70 

10.94 

11.20 

11.45 

11.70 

11.95 

12.20 

12.45 

12.70 

12.96 

13.21 

13.46 

3.75 

11.00 

11.26 

11.51 

11.76 

12.01 

12.26 

12.51 

12.76 

13.02 

13.27 

13.52 

3.80 

11.06 

11.32 

11.57 

11.82 

12.07 

12.32 

12.57 

12.82 

13.08 

13.33 

13.58 

3.85 

11.12 

11.38 

11.63 

11.88 

12.13 

12.38 

12.63 

12.88 

13.14 

13.39 

13.64 

3.90 

11.18 

11.44 

11.69 

11.94 

12.19 

12.44 

12.69 

12.94 

13.20 

13.45 

13.70 

3.95 

11.24 

11.50 

11.75 

12.00 

12.25 

12.50 

12.75 

13.00 

13.26 

13.51 

13.77 

4.00 

11.30 

11.56 

11.81 

12.06 

12.31 

12.56 

12.81 

13.06 

13.32 

13.57 

13.83 

4.05 

11.36 

11.62 

11.87 

12.12 

12.37 

12.62 

12.87 

13.12 

13.38 

13.63 

13.89 

4.10 

11.42 

11.68 

11.93 

12.18 

12.43 

12.68 

12.93 

13.18 

13.44 

13.69 

13.95 

4.15 

11.48 

11.74 

11.99 

12.24 

12.49 

12.74 

12.99 

13.25 

13.50 

13.76 

14.01 

4.20 

11.54 

11.80 

12.05 

12.30 

12.55 

12.80 

13.05 

13.31 

13.56 

13.82 

14.07 

4.25 

11.60 

11.86 

12.11 

12.36 

12.61 

12.86 

13.12 

13.37 

13.62 

13.88 

14.13 

4.30 

11.66 

11.92 

12.17 

12.42 

12.67 

12.92 

13.18 

13.43 

13.68 

13.94 

14.19 

4.35 

11.72 

11.98 

12.23 

12.48 

12.73 

12.98 

13.24 

13.49 

13.74 

14.00 

14.25 

4.40 

11.78 

12.04 

12.29 

12.54 

12.79 

13.04 

13.30 

13.55 

13.80 

14.06 

14.31 

4.45 

11.84 

12.10 

12.35 

12.60 

12.85 

13.10 

13.36 

13.61 

13.86 

14.12 

14.37 

TABLE  FOB  DETERMINING  TOTAL  SOLIDS  IN  MILK   FROM  ANY   GIVEN  SPECIFIC 
GRAVITY  AND  PERCENTAGE  OF  FAT — Continued 


Per 

cent- 

Lactometer  reading  at  60°  F.  (Quevenne  degrees). 

age  oi 

fat 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

Per 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

total 

total 

total 

total 

total 

total 

total 

total 

total 

total 

total 

solids 

Solid! 

solids 

solids 

solids 

solids 

solids 

solids 

solids 

solids 

solids 

4.50 

11.90 

12.16 

12.41 

12.66 

12.91 

13.16 

13.42 

13.67 

13.92 

14.18 

14.43 

4.55 

11.97 

12.22 

12.47 

12.72 

12.97 

13.22 

13.48 

13.73 

13.98 

14.24 

14.49 

4.60 

12.03 

12.28 

12.53 

12.78 

13.03 

13.28 

13.54 

13.79 

14.04 

14.30 

14.55 

4.65 

12.09 

12.34 

12.59 

12.84 

13.09 

13.34 

13.60 

13.85 

14.10 

14.36 

14.61 

4.70 

12.15 

12.40 

12.65 

12.90 

13.15 

13.40 

13.66 

13.91 

14.16 

14.42 

14.67 

4.75 

12.21 

12.46 

12.71 

12.96 

13.21 

13.46 

13.72 

13.97 

14.22 

14.48 

14.73 

4.80 

12.27 

12.52 

12.77 

13.02 

13.27 

13.52 

13.78 

14.03 

14.28 

14.54 

14.79 

4.85 

12.33 

12.58 

12.83 

13.08 

13.33 

13.58 

13.84 

14.09 

14.34 

14.60 

14.85 

4.90 

12.39 

12.64 

12.89 

13.14 

13.39 

13.64 

13.90 

14.15 

14.40 

14.66 

14.91 

4.95 

12.45 

12.70 

12.95 

13.20 

13.45 

13.70 

13.96 

14.21 

14.46 

14.72 

14.97 

5.00 

12.51 

12.76 

13.01 

13.26 

13.51 

13.76 

14.02 

14.27 

14.52 

14.78 

15.03 

5.05 

12.57 

12.82 

13.07 

13.32 

13.57 

13.83 

14.08 

14.33 

14.58 

14.84 

15.09 

5.10 

12.63 

12.88 

13.13 

13.38 

13.63 

13.89 

14.14 

14.39 

14.64 

14.90 

15.15 

5.15 

12.69 

12.94 

13.19 

13.44 

13.69 

13.95 

14.20 

14.45 

14.70 

14.96 

15.21 

5.20 

12.75 

13.00 

13.25 

13.50 

13.75 

14.01 

14.26 

14.51 

14.76 

15.02 

15.27 

5.25 

12.81 

13.06 

13.31 

13.56 

13.81 

14.07 

14.32 

14.57 

14.82 

15.08 

15.33 

5.30 

12.87 

13.12 

13.37 

13.62 

1387 

14.13 

14.38 

14.63 

14.88 

15.14 

15.39 

5.35 

12.93 

13.18 

13.43 

13.68 

13.93 

14.19 

14.44 

14.70 

14.95 

15.20 

15.45 

5.40 

12.99 

13.24 

13.49 

13.74 

14.00 

14.25 

14.50 

14.76 

15.01 

15.26 

15.51 

5.45 

13.05 

13.30 

13.55 

13.80 

14.06 

14.31 

14.56 

14.82 

15.07 

15.32 

15.57 

5.50 

13.11 

13.36 

13.61 

13.86 

14.12 

14.37 

14.62 

14.88 

15.13 

15.38 

15.63 

5.55 

13.17 

13.42 

13.67 

13.93 

14.18 

14.43 

14.69 

14.94 

15.19 

15.44 

15.69 

5.60 

13.23 

13.48 

13.73 

13.99 

14.24 

14.49 

14.75 

15.00 

15.25 

15.50 

15.75 

5.65 

13.29 

13.54 

13.79 

14.05 

14.30 

14.55 

14.81 

15.06 

15.31 

15.56 

15.81 

5.70 

13.35 

13.60 

13.85 

14.11 

14.36 

14.61 

14.87 

15.12 

15.37 

15.62 

15.87 

5.75 

13.41 

13.66 

13.91 

14.17 

14.42 

14.68 

14.93 

15.18 

15.43 

15.68 

15.93 

5.80 

13.47 

13.72 

13.97 

14.23 

14.48 

14.74 

14.99 

15.24 

15.49 

15.74 

15.99 

5.85 

13.53 

13.78 

14.04 

14.29 

14.54 

14.80 

15.05 

15.30 

15.55 

15.80 

16.06 

5.90 

13.59 

13.84 

14.10 

14.35 

14.60 

14.86 

15.11 

15.36 

15.61 

15.86 

16.12 

5.95 

13.65 

13.90 

14.16 

14.41 

14.66 

14.92 

15.17 

15.42 

15.67 

15.92 

16.18 

6.00 

13.71 

13.96 

14.22 

14.47 

14.72 

14.98 

15.23 

15.48 

15.73 

15.98 

16.24 

6.05 

13.77 

14.02 

14.28 

14.53 

14.78 

15.04 

15.29 

15.54 

15.79 

16.04 

16.30 

6.10 

13.83 

14.08 

14.34 

14.59 

14.84 

15.10 

15.35 

15.60 

15.85 

16.10 

16.35 

6.15 

13.89 

14.14 

14.40 

14.65 

14.90 

15.16 

15.41 

15.66 

15.91 

16.16 

16.42 

6.20 

13.95 

14.20 

14.46 

14.71 

14.96 

15.22 

15.47 

15.72 

15.97 

16.22 

16.48 

6.25 

14.01 

14.26 

14.52 

14.77 

15.02 

15.28 

15.53 

15.78 

16.03 

16.28 

16.54 

6.30 

14.07 

14.32 

14.58 

14.83 

15.08 

15.34 

15.59 

15.84 

16.09 

16.34 

16.60 

6.35 

14.13 

14.38 

14.64 

14.90 

15.14 

15.40 

15.65 

15.90 

16.15 

16.40 

16.66 

6.40 

14.19 

14.44 

14.70 

14.96 

15.20 

15.46 

15.71 

15.96 

16.21 

16.46 

16.72 

6.45 

14.25 

14.50 

14.76 

15.02 

15.26 

15.52 

15.77 

16.02 

16.27 

16.52 

16.78 

6.50 

14.31 

14.56 

14.82 

15.08 

15.32 

15.58 

15.83 

16.08 

16.33 

16.58 

16.84 

6.55 

14.37 

14.62 

14.88 

15.14 

15.38 

15.64 

15.89 

16.14 

16.39 

16.64 

16.90 

6.60 

14.43 

14.68 

14.94 

15.20 

15.44 

15.70 

15.95 

16.20 

16.45 

16.70 

16.96 

6.65 

14.49 

14.74 

15.00 

15.26 

15.50 

15.76 

16.01 

16.26 

16.51 

16.76 

17.02 

6.70 

14.55 

14.80 

15.06 

15.32 

15.56 

15.82 

16.07 

16.32 

16.57 

16.82 

7.08 

6.75 

14.61 

14.86 

15.12 

15.38 

15.62 

15.88 

16.13 

16.38 

16.63 

16.88 

7.14 

6.80 

14.67 

14.92 

15.18 

15.44 

15.68 

15.94 

16.19 

6.44 

16.69 

16.94 

7.20 

6.85 

14.73 

14.98 

15.24 

15.50 

15*74 

16.00 

16.25 

6.50 

16.75 

7.00 

7.26 

6.90 

14.79 

15.04 

15.30 

15.56 

15.80 

16.06 

16.31 

6.56 

16.81 

7.06 

7.32 

6.95 

14.85 

15.10 

15.36 

15.62 

15.86 

16.12 

16.37 

6.62 

6.87 

7.12 

7.38 

METHODS  OF  EXAMINING  MILK 

PROPORTIONAL  PARTS 


245 


Fraction  to 

Fraction  to 

Fraction  to 

Lactometer 

be  added 

Lactometer 

be  added 

Lactometer 

be  added 

fraction 

to  total 

fraction 

to  total 

fraction 

to  total 

solids 

solids 

solids 

0.1 

0.03 

0.4 

0.10 

0.7 

0.18 

.2 

.05 

.5 

.13 

.8 

.20 

.3 

.08 

.6 

.15 

.9 

.23 

A  simpler  but  less  accurate  formula  by  Babcock  is 
based  on  the  fact  that  the  per  cent,  of  total  solids  in- 
creases at  about  the  rate  of  0.25  for  each  lactometer 
(Quevenne)  degree  and  1.2  for  each  per  cent,  of  fat. 
This  formula  is  as  follows. 

Per  cent,  total  solids  =  %  L  +  (1.*  f) 

L  =  lactometer  reading  (Quevenne  degrees);  f  =»  fat  percent. 

By  Automatic  Reckoner. — The  per  cent,  of  total 
solids  can  also  be  determined,  when  the  specific  gravity 
and  fat  per  cent,  are  known,  by  means  of  Ackermann's 
automatic  reckoner  and  Richmond's  sliding  rule.  The 
former  is  based  upon  Fleischmann's  formula  and  the 
latter  upon  Richmond's  formula.  These  two  formulas 
do  not  give  quite  as  accurate  results  as  the  Babcock  for- 
mula on  page  242. 

DETERMINATION  OF  SOLIDS  NOT  FAT 

When  the  per  cent,  of  fat  and  of  total  solids  is 
known,  the  per  cent,  of  solids  not  fat  can  be  determined 
by  simply  subtracting  the  per  cent,  of  fat  from  the  per 
cent,  of  total  solids.  The  per  cent,  of  solids  not  fat  can 
also  be  closely  calculated  from  the  fat  per  cent,  and  the 
specific  gravity  by  means  of  Babcock' s  formula  (page 
242) .  The  per  cent,  of  solids  not  fat  in  normal  market 
milk  ranges  from  8.5  to  10.5. 


246        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 
DETERMINATION  OF  THE  SPECIFIC  GRAVITY  OF  THE  SOLIDS 

The  specific  gravity  of  the  dry  milk  solids  can  be  cal- 
culated from  the  per  cent,  of  total  solids  and  the  specific 
gravity  of  the  milk  according  to  the  following  formula: 

st 

mS%t-  (100s  -100) 
m  represents  dry  milk  solids,  s  specific  gravity  and  t  total  solids. 

The  specific  gravity  of  the  dry  solids  of  normal  whole 
milk  varies  from  1.31  to  1.36.  Skimming  milk  increases 
the  specific  gravity  of  the  milk  solids. 

DETERMINATION  OF  THE  PER  CENT.  OF  FAT  IN  THE 
TOTAL  SOLIDS 

The  per  cent,  of  fat  in  the  total  solids  can  be  calcu- 
lated from  the  per  cent,  of  fat  and  of  total  solids  in  the 
milk  according  to  the  following  formula: 

P=YX  10° 

p  represents  per  cent,  of  fat  in  total  solids,  f  per  cent,  of  fat  in  the  milk  and 
t  per  cent,  of  total  solids. 

The  per  cent,  of  fat  in  the  total  solids  varies  from 
20  to  34.  It  is  decreased  by  skimming. 

DETERMINATION  OF  THE  DEGREE  OF  ADULTERATION 

When  it  is  possible  to  compare  a  sample  of  adulter- 
ated milk  with  a  sample  of  the  same  milk  collected  under 
conditions  which  exclude  the  possibility  of  adulteration, 
the  extent  of  the  adulteration  may  be  determined  approxi- 
mately by  the  following  formulas  of  Bohmlander: 


E 


-«•(>-£) 


METHODS  OF  EXAMINING  MILK  247 

In  the  first  formula  W  is  the  per  cent,  of  water  in 
the  unadulterated  sample;  w  is  the  per  cent,  of  water 
in  the  adulterated  sample;  R  is  the  per  cent,  of  solids 
not  fat  in  the  unadulterated  sample ;  r  is  the  per  cent,  of 
solids  not  fat  in  the  adulterated  sample;  M  represents 
the  quantity  of  water  to  100  grammes  of  milk. 

In  the  second  formula  F  is  the  per  cent,  of  fat  in  the 
unadulterated  sample;  f  is  the  per  cent,  of  fat  in  the 
adulterated  sample;  R  is  the  per  cent,  of  solids  not  fat 
in  the  unadulterated  sample ;  r  is  the  per  cent,  of  solids 
not  fat  in  the  adulterated  sample,  and  E  represents  the 
per  cent,  of  fat  removed  by  skimming. 

TESTS  FOR  NITRATES  AND  NITRITES 

Soachlet's  Test. — One-half  c.c.  of  a  20  per  cent,  cal- 
cium chloride  solution  is  mixed  with  about  30  c.c.  of  milk 
and  the  mixture  is  boiled  and  filtered.  A  2  per  cent, 
solution  of  diphenylamin  in  chemically  pure  sulphuric 
acid  is  added  in  sufficient  quantity  to  some  of  the  filtrate 
to  make  it  milky.  Chemically  pure  sulphuric  acid  is  then 
poured  slowly  down  the  side  of  the  test  tube  so  that  it 
forms  a  layer  at  the  bottom.  If  nitrates  or  nitrites  are 
present  a  blue  zone  is  formed  at  the  point  where  the  two 
fluids  come  in  contact.  This  test  will  detect  one  part  of 
nitrates  in  100,000;  most  farm  water  contains  one  part 
in  10,000  (Jensen). 

A  modification  of  this  test  is  described  by  Rievel  as 
follows :  Place  a  small  quantity  of  milk  in  a  test  tube  and 
then  pour  in  slowly,  so  that  the  two  fluids  will  not  mix, 
a  solution  of  diphenylamin  in  chemically  pure  sulphuric 
acid  (1 : 10) .  If  minute  traces  of  nitrites  are  present  a 
blue  ring  will  form  at  the  point  of  contact  of  the  two 
fluids. 


248        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Fritzmanrfs  Method. — Place  2  c.c.  of  milk  in  a  test 
tube  and  slowly  run  down  the  side  2  c.c.  of  pure  sul- 
phuric acid  to  which  one  drop  of  a  dilute  formalin  solu- 
tion has  been  added.  In  the  presence  of  nitrites  a  blue- 
violet  ring  will  form  at  the  point  of  contact  of  the  two 
fluids,  but  the  reaction  will  not  occur  in  the  presence  of 
albumen.  According  to  Riegel  a  suitable  formalin  solu- 
tion may  be  made  by  adding  one  drop  of  40  per  cent, 
formalin  to  300  c.c.  of  distilled  water  and  mixing  15 
grammes  of  this  solution  with  one  litre  of  concentrated 
sulphuric  acid.  This  method  gives  very  accurate  results 
and  is  easily  carried  out  (Rievel). 

Fresh,  clean  milk  does  not  contain  nitrites.  Ac- 
cording to  Jensen,  nitrites  are  not  present  in  the  milk 
even  when  they  have  been  contained  in  the  food  or  drink- 
ing water  of  the  cow.  Marcus  and  Huyge  assert  that  if 
nitrate  of  potassium  is  administered  to  the  cow  in  quan- 
tities of  5  to  10  grammes  the  milk  sometimes  contains 
nitrates.  It  would  seem  likely  that  nitrates  would  also 
be  excreted  through  the  udder  if  the  cow  obtained  access 
to  fertilizer  containing  nitrates  or  to  sacks  which  had  con- 
tained such  fertilizer. 

The  demonstration  of  nitrates  or  nitrites  in  milk  is 
generally  regarded  as  evidence  that  water  has  been  added 
to  the  milk.  Most  farm  waters  contain  nitrates  and 
nitrites,  as  do  also  some  city  water  supplies.  But  Rievel 
points  out  that  the  presence  of  nitrates  or  nitrites  in  milk 
cannot  be  regarded  as  positive  proof  that  the  milk  has 
been  watered,  because  when  milk  vessels  are  merely 
rinsed  with  water  containing  nitrates  or  nitrites  the  milk 
may  give  a  positive  reaction  if  the  water  is  quite  rich  in 
nitrates  or  nitrites.  Tillmans  says  that  normal  milk  may 


METHODS  OF  EXAMINING  MILK 


249 


contain  up  to  1  to  2  mg.  per  litre  from  this  source.  Rievel 
also  states  that  a  positive  reaction  may  occur  with  milk 
soiled  with  manure,  but  Tillmans  has  never  found  dirty 
milk  to  give  any  indication  of  containing  more  nitrates 
or  nitrites  than  milk  from  vessels  that  had  been  washed 
with  water  rich  in  nitrates  or  nitrites.  A  negative  reac- 
tion to  the  nitrate  test  is  no  evidence  that  the  milk  has  not 
been  watered,  as  water  free  from  these  substances  may 
be  used  for  dilution.  According  to  Utz,  milk  to  be 
tested  for  nitrates  should  be  boiled  unless  the  test  can 
be  made  at  once,  because  the  action  of  the  lactic  acid- 
forming  bacteria  may  reduce  the  nitrates  or  cause  them 
to  disappear  entirely. 

DETECTION  OF  THE  USUAL  ADULTERATIONS 

When  milk  is  adulterated,  it  is  usually  by  partial 
skimming,  dilution  with  skimmed  milk,  or  dilution  with 
water.  The  changes  caused  by  these  various  forms  of 
adulteration  are  shown  in  the  following  table,  which  is 
taken  from  Jensen's  Milk  Hygiene: 


Specific 
gravity 
of  the 
milk 

Per- 
centage 
of  fat 

Percent- 
age of 
soli  da 
not  fat 

Specific 
gravity 
of  the 
milk 
solids 

Per- 
centage 
of  fat 
in  the 
total 
solids 

Per- 
centage 
of  ash 

Presence 
or  absence 
of  nitrate 

Normal  milk                 .  I 

1.029  to 
1.034 
aver. 
1.032 

Higher 

Lower 

Little 
change 

3  to  5 

Lower 
Lower 
Lower 

8.5  to 
10.5 

Very 
slightly 
higher 

Lower 
Lower 

1.30  to 
1.34 

Higher 

No 
change 

Higher 

20  to 
34 

Lower 

No 
change 

Lower 

0.7  to 
0.75 

Higher 
Lower 
Lower 

0 

0 
+  orO 

+  orO 

Skimmed    or    diluted  f 
with  skimmed  milk-j 

Water  added  f 

Skimmed    and    water  / 
added  \ 

250        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

Starch,  flour,  viscogen,  etc.,  may  be  added  to  skimmed 
milk  or  cream  to  increase  the  viscosity  (see  page  33) . 

The  test  for  starch  is  made  as  follows:  Add  a  few 
drops  of  acetic  acid  to  the  milk  or  cream,  boil  and  filter. 
To  the  filtrate  add  a  few  drops  of  a  dilute  iodine  solution. 
If  starch  is  present  the  filtrate  becomes  blue. 

The  presence  of  viscogen  is  indicated  by  a  high  per 
cent,  of  salts. 

DETERMINATION  OF  THE  REFRACTION  NUMBER 

The  most  satisfactory  milk  serum  for  this  test  is  ob- 
tained by  Ackermann's  calcium  chloride  method  and  the 
refractive  index  is  most  conveniently  determined  by 
Zeiss'  dipping  ref ractometer.  The  method  is  as  follows : 

30  c.c.  of  the  milk  to  be  tested  is  placed  in  a  test 
tube  of  75  c.c.  capacity  and  mixed  with  0.25  c.c.  of  a 
1  to  10  solution  of  calcium  chloride  in  distilled  water 
(specific  gravity  1.1375  and  refraction  number  26  at 
17.5°  C.).  The  test  tube  is  closed  with  a  perforated 
rubber  stopper,  then  connected  with  a  22  c.c.  condenser 
and  heated  for  15  minutes  in  a  bath  of  briskly  boiling 
water.1  It  is  then  placed  in  cold  water  and  cooled.  Dur- 
ing this  process  the  serum  separates  from  the  curd  and  is 
poured  off  into  a  beaker.  If  the  serum  is  not  sufficiently 
free  of  coagula  to  permit  of  the  passage  of  adequate 
light,  it  is  an  indication  that  acid  fermentation  has  ad- 
vanced too  far  for  the  milk  to  be  investigated  with  the 
refractometer,  the  loss  of  lactose  suffered  in  such  cases 
being  sufficient  to  render  the  result  inaccurate.  The 
beaker  containing  the  serum  is  placed  in  the  water  bath 

1  If  the  milk  tube  is  not  connected  with  a  condenser  the 
result  of  the  test  will  be  nearly,  if  not  exactly,  the  same  and 
the  test  is  much  simplified. 


METHODS  OF  EXAMINING  MILK 


251 


of  the  refractometer.  The  temperature  of  the  water 
bath  should  be  17.5°  C.  After  allowing  8  to  10  minutes 
for  the  serum  in  the  beaker  to  reach  the  same  tempera- 
ture, the  prism  of  the  refractometer  is  inserted  in  the 
beaker  and  the  refraction  number  is  read  from  the  scale, 


Fia.  38. — Zeiss  dipping  refractometer. 

which  is  located  in  the  refractometer  beneath  the  ocular. 
On  looking  into  the  ocular  it  will  be  observed  that  a  por- 
tion of  the  field  is  dark  and  the  remainder  light.  The 
border  line  is  usually  fringed  with  colors  and  the  com- 
pensator must  then  be  rotated  by  means  of  the  milled 


252        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

ring  on  the  barrel  of  the  refractometer  until  the  line  of 
demarcation  between  the  dark  and  light  areas  is  sharply 
defined  and  colorless.  When  this  line  falls  on  one  of  the 
divisions  of  the  scale  it  is  merely  necessary  to  note  the 
number,  which  is  then  the  refraction  number.  When  the 
line  falls  between  two  divisions  of  the  scale  the  scale  is 
then  moved  towards  the  border  line  by  turning  the  thumb 
screw  of  the  micrometer  below  the  ocular  until  the  scale 
division  which  was  nearest  to  the  border  line  on  the  dark 
side  is  exactly  on  it.  The  figure  opposite  the  indicator 
on  the  micrometer  is  then  noted  and  is  added  to  the 
figure  of  the  scale  division  as  a  decimal.  For  example, 
if  the  figure  opposite  the  scale  division  nearest  to  the 
border  line  on  the  dark  side  was  38  and  the  micrometer 
was  rotated  to  7  in  moving  the  scale  division  to  the 
border  line,  then  the  refraction  number  is  38.7  The 
refraction  number  can  be  converted  into  the  refractive 
index  by  means  of  a  formula  furnished  with  the  refrac- 
tometer, but  this  is  not  necessary. 

Before  beginning  the  examination  of  a  number  of 
samples  of  milk,  the  refractometer  should  be  tested  with 
distilled  water,  which  at  17.5°  C.  should  give  a  reading 
of  15.5.  The  water  bath  is  made  to  hold  12  beakers 
at  one  time  so  that  when  a  number  of  samples  are  to 
be  examined  there  will  be  an  opportunity  for  each  one 
to  reach  the  required  temperature  without  delaying  the 
examinations.  When  the  prism  of  the  refractometer  is 
removed  from  one  sample,  or  from  the  distilled  water, 
it  should  be  wiped  dry  with  a  soft  linen  cloth  before  being 
introduced  into  another. 

The  refraction  number  of  normal  market  milk  is  in 
most  cases  between  38  and  40.5.  In  rare  cases  it  may 
be  as  low  as  37.3  and  in  one  case  reported  by  Mai  and 


METOHDS  OF  EXAMINING  MILK  253 

Rothenfusser  it  reached  41.5.  The  addition  of  a  small 
quantity  of  water  to  milk  lowers  the  refraction  number, 
but  on  account  of  the  wide  range  in  the  refraction  number 
of  normal  market  milk  it  is  necessary,  in  order  to  detect 
slight  additions  of  water,  to  have  the  herd  under  suspicion 
milked  under  supervision  and  to  take  a  sample  of  the 
milk  and  compare  the  refraction  number  of  this  sample 
with  the  refraction  number  of  the  sample  of  market  milk. 
The  daily  variation  in  the  refraction  number  of  the  milk 
of  a  herd  will  not  exceed  0.1  to  0.55.  Changes  of  feed 
have  only  a  slight  influence  and  incomplete  milking  has 
no  effect.  When  the  refraction  number  is  as  low  as  36.5 
or  below  the  milk  may  be  unhesitatingly  pronounced 
watered. 

The  refraction  number  is  not  affected  by  the  per 
cent,  of  fat.  A  sample  of  milk  taken  from  the  top  of  a 
can  and  one  taken  from  the  bottom  of  the  same  can  will 
both  have  exactly  the  same  refraction  number,  although 
there  will  be  a  great  difference  in  the  fat  per  cent.  This  is 
an  important  advantage,  because  when  a  charge  that  milk 
has  been  watered  is  based  on  the  specific  gravity  and  fat 
per  cent,  the  claim  is  often  made  that  the  sample  was 
taken  from  the  bottom  of  the  can  or  after  the  top  milk 
had  been  sold. 

The  presence  of  boric  acid  and  borax  in  the  propor- 
tion usually  used  to  preserve  milk  (0.1  to  0.2  per  cent.) 
will  increase  the  refraction  of  the  milk  serum.  Salicylic 
acid  also  increases  the  refraction  when  present  in  as 
small  amount  as  0.05  per  cent,  which  is  the  quantity  used 
as  a  preservative,  but  formaldehyde  causes  no  increase 
when  present  in  the  amount  ordinarily  used  as  a  preserva- 
tive. Sodium  bicarbonate  does  not  have  any  effect  when 
added  up  to  0.1  per  cent. 


254        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

In  individual  milk  from  diseased  cows  the  refraction 
number  has  been  found  to  be  decreased  in  tuberculosis, 
febrile  diseases,  foot  and  mouth  disease,  and  mastitis.  In 
some  cases  of  streptococcic  mastitis  Obladen  found  it  as 
low  as  24.8.  The  effect  of  mixing  milk  from  diseased 
cows  with  normal  milk  has  not  been  determined,  but  since 
diseased  milk  and  watered  milk  are  both  low  in  refraction 
there  is  a  possibility  of  confusion  unless  a  proper  investi- 
gation is  made. 

DETERMINATION  OF  THE  REACTION 

Litmus  Test. — A  strip  of  red  and  a  strip  of  blue  lit- 
mus paper  are  dipped  in  the  milk  for  a  few  seconds  and 
the  color  of  the  wet  and  dry  portions  is  compared.  Nor- 
mal milk,  when  drawn  from  the  udder,  is  amphoteric  to 
litmus,  i.e.,  the  blue  litmus  is  changed  to  red  and  the  red 
litmus  to  blue.  If  the  milk  is  more  acid  than  normal,  the 
blue  paper  will  be  colored  red  but  the  red  paper  will  not 
be  changed,  while  if  the  alkalinity  is  increased  the  red 
paper  will  be  colored  blue  and  the  blue  paper  will  not 
be  changed.  Individual  milk  is  frequently  alkaline  to 
litmus  in  the  last  stages  of  lactation;  it  also  gives  an 
alkaline  reaction  in  most  cases  of  mastitis,  but  in  some 
cases  it  is  acid.  Market  milk  is  usually  acid  to  litmus ;  it 
is  never  alkaline  except  when  an  alkali  has  been  added. 
The  litmus  test  is  only  of  value  as  a  preliminary  test 
for  individual  milk. 

Mann's  Acidity  Test.— The  apparatus  required  for 
this  test  is  a  50  c.c.  burette  with  a  stopcock,  a  stand,  a 
beaker  or  a  white  cup,  a  stirring  rod,  and  a  50  c.c.  pipette. 
The  reagents  required  are  a  solution  of  phenolphthalein 
and  a  one-tenth  normal  solution  of  sodium  hydroxide. 
The  phenolphthalein  solution  is  prepared  by  dissolving 


METHODS  OF  EXAMINING  MILK  255 

10  grammes  of  powdered  phenolphthalein  in  300  c.c.  of 
90  per  cent,  alcohol.  The  one-tenth  normal  (Yio)  solu- 
tion of  sodium  hydroxide  (NaOH)  should  be  prepared 
and  standardized  as  directed  by  the  U.  S.  Pharmacopoeia. 
Each  cubic  centimetre  of  this  solution  contains  sufficient 
sodium  hydroxide  (0.004  gramme)  to  neutralize  0.009 
gramme  of  lactic  acid. 

After  thoroughly  mixing  the  milk  or  cream  to  be 
tested,  50  c.c.  are  measured  into  the  beaker  or  cup  with 
the  pipette.  The  pipette  is  then  filled  to  the  50  c.c.  mark 
with  water,  preferably  distilled,  which  is  added  to  the 
milk  or  cream.  This  is  done  for  the  purpose  of  rinsing 
all  milk  or  cream  from  the  pipette.  Five  to  ten  drops  of 
the  phenolphthalein  solution  are  then  placed  in  the  beaker 
or  cup  and  the  fluid  is  mixed  by  stirring  with  a  glass  rod. 
The  tenth  normal  sodium  hydroxide  solution  is  run  into 
the  beaker  or  cup  drop  by  drop,  stirring  frequently,  until 
a  pink  color  appears  and  remains  permanently.  The 
amount  of  sodium  hydroxide  solution  used  is  then  read 
off  from  the  burette. 

The  result  of  the  test  may  be  expressed  in  degrees 
or  in  per  cent  of  acidity.  Degrees  of  acidity  correspond 
to  the  number  of  c.c.  of  tenth-normal  sodium  hydroxide 
solution  used  to  the  hundred  c.c.  of  milk  or  cream.  The 
per  cent,  of  acidity  may  be  obtained  by  the  following 
calculation: 


_ 
No.  c.c.  milk  or  cream  used 


For  example,  if  9  c.c.  of  the  one-tenth  normal  solu- 
tion are  used  in  testing  50  c.c.  of  milk  or  cream,  then 


X  100  «  9  X  0.018  «  0.16  per  cent,  acidity. 


256        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

If  the  reaction  is  alkaline,  i.e.,  if  the  milk  or  cream 
becomes  permanently  pink  when  the  phenolphthalein 
solution  is  added,  or  if  the  pink  color  appears  and  remains 
before  the  addition  of  the  quantity  of  tenth-normal 
sodium  hydroxide  solution  required  for  normal  milk,  then 
the  rosolic  acid  test  for  alkalies  should  be  applied  (see 
page  260). 

Acidity  Test  With  Babcock  Pipette. — The  test  for 
acidity  may  also  be  made  by  using  a  Babcock  fat-test 
pipette  to  measure  the  milk  or  cream.  17.6  c.c.  of  milk 
or  cream  is  placed  in  the  cup  or  beaker,  a  few  drops  of 
the  phenolphthalein  solution  added  and  the  tenth-normal 
solution  of  sodium  hydroxide  run  in  slowly  until  the  pink 
color  appears  and  remains  permanently.  The  per  cent, 
of  acid  may  be  determined  by  dividing  the  number  of  c.c. 
of  tenth-normal  sodium  hydroxide  solution  used  by  two, 
and  expressing  the  quotient  in  tenths,  thus: 

6  -T-  2  =  3,  or  0.3  per  cent.  acid. 

Farringtorfs  Alkaline  Tablet  Test. — The  special 
feature  of  this  test  is  the  use  of  tablets  of  sodium  car- 
bonate for  making  the  alkaline  solution.  Each  tablet 
contains  sufficient  alkali  to  neutralize  0.034  gramme  of 
acid.  Five  tablets  are  placed  in  a  100  c.c.  graduated 
cylinder  and  clean,  soft  water,  preferably  distilled,  is 
added  up  to  the  97  c.c.  mark.  The  cylinder  is  then 
closed  tightly  with  a  stopper  and  laid  on  its  side  for  sev- 
eral hours  to  give  the  tablets  an  opportunity  to  dissolve. 
Solution  is  never  entirely  complete,  a  slight  flocculent 
residue  remaining.  After  thoroughly  mixing  by  shaking, 
17.6  c.c.  of  the  milk  or  cream  to  be  tested  is  measured 
into  the  beaker  or  cup  with  a  Babcock  fat-test  pipette. 
The  pipette  is  then  filled  with  water  to  the  17.6  mark 


METHODS  OF  EXAMINING  MILK  257 

to  rinse  it  and  this  is  added  to  the  milk  or  cream.  A  few 
drops  of  phenolphthalein  solution  are  added  and  the 
alkali  solution  in  the  cylinder,  after  thorough  shaking, 
is  added  to  the  mixture  in  the  cup  or  beaker  until  the 
pink  color  remains  permanent.  The  number  of  c.c.  used 
is  then  read  off  from  the  measuring  cylinder.  Each  c.c. 
represents  one-tenth  per  cent,  of  acid  in  the  sample 
tested. 

TESTS  FOR  PRESERVATIVES 

The  use  of  antiseptics  to  inhibit  bacterial  growth  and 
thus  prevent  the  souring  or  decomposition  of  milk  is 
much  less  common  than  formerly,  but  is  still  practised 
to  some  extent.  This  is  also  true  of  the  addition  of 
alkalies  to  neutralize  acidity  and  delay  curdling.  Not 
only  may  the  antiseptics  do  harm  themselves,  but  they 
and  the  alkalies  conceal  conditions  in  milk  which  are  un- 
desirable and  may  prove  injurious.  For  these  reasons, 
the  addition  of  these  substances  to  milk  is  forbidden 
by  Federal  and  State  laws. 

A  simple  test  for  preservatives  may  be  made  by 
setting  a  sample  of  milk  aside  and  observing  if  it  curdles 
within  the  usual  time.  If  it  does  not,  the  presence  of 
preservatives  or  alkalies  may  be  suspected.  The  pre- 
servatives most  commonly  used  and  tests  for  detecting 
their  presence  are  given  below. 

Boric  Acid  and  Borax. — Until  the  introduction  of  for- 
maldehyde, boric  acid  and  borax  were  the  most  popular 
preservatives;  0.1  to  0.2  per  cent,  of  these  substances  will 
delay  the  curdling  of  milk  for  several  days.  They  may  be 
detected  by  the  following  tests : 

Vllllers'  and  Fayolle's  Test. — About  10  c.c.  of  the 
milk  is  placed  in  a  porcelain  crucible,  evaporated  to  dry- 
ness  and  the  residue  burned  to  an  ash.  Sufficient  sul- 

17 


258         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

phuric  acid  to  make  a  paste  is  added  to  the  ash  and  3 
c.c.  of  methyl  alcohol  is  mixed  with  it.  The  vapor  which 
is  then  given  off  is  ignited.  If  boric  acid  or  borax  is 
present,  even  in  very  small  quantity,  the  flame  will  be 
green. 

Turmeric  Test. — Add  6  or  7  drops  of  hydrochloric 
acid  to  10  c.c.  of  milk  and,  after  coagulation  has  occurred, 
filter.  Dip  a  piece  of  turmeric  paper  into  the  filtrate  and 
allow  it  to  dry.  If  boric  acid  is  present  in  the  proportion 
of  0.02  per  cent,  or  borax  in  the  proportion  of  0.03  per 
cent.,  the  paper  will  be  colored  cherry-red  (Kiihl) ;  this 
color  will  be  changed  to  bluish-black  by  ammonia  water. 

Another  method  of  applying  the  turmeric  test  is  de- 
scribed by  Farrington  and  Woll  as  follows :  "  One  hun- 
dred cubic  centimetres  of  milk  are  made  alkaline  with 
a  soda  or  potash  solution  and  then  evaporated  to  dryness 
and  incinerated.  The  ash  is  dissolved  in  water,  to  which 
a  little  hydrochloric  acid  has  been  added,  and  the  solu- 
tion filtered.  A  strip  of  turmeric  paper  moistened  with 
the  filtrate  will  be  colored  reddish-brown  when  dried  at 
100°  C.  on  a  watch  glass  if  boric  acid  is  present." 

Formaldehyde. — Formaldehyde,  the  favorite  preserva- 
tive for  milk,  is  used  in  the  form  of  formaldehyde  solution, 
formalin,  formol,  etc.  A  very  small  quantity  (0.008  per 
cent,  of  formaldehyde,  0.02  per  cent,  of  formalin)  will 
prevent  curdling  for  four  days.  The  following  tests  may 
be  used  for  detecting  the  presence  of  formaldehyde : 

Richmond's  Test. — Place  a  small  quantity  of  milk 
in  a  test  tube,  add  an  equal  quantity  of  water  and  then 
pour  a  little  commercial  sulphuric  acid  slowly  down  the 
side  of  the  tube  so  that  it  will  form  a  layer  at  the  bottom. 
A  bluish  or  violet  ring  at  the  point  where  the  acid  and 
milk  come  in  contact  indicates  the  presence  of  formalde- 
hyde. If  no  formaldehyde  is  present  a  faint,  greenish 


METHODS  OF  EXAMINING  MILK  259 

ring  is  formed.  This  test  will  detect  1  part  of  formalde- 
hyde in  200,000  parts  of  milk. 

Leach's  Test. —  The  reagent  used  in  this  test  is  a  solu- 
tion of  hydrochloric  acid  and  ferric  chloride  consisting  of 
998  c.c.  of  hydrochloric  acid  of  a  specific  gravity  of  1.2, 
and  2  c.c.  of  a  10  per  cent,  aqueous  solution  of  ferric 
chloride.  Place  about  10  c.c.  of  milk  and  an  equal  quan- 
tity of  this  solution  in  a  white  cup  or  casserole  and  slowly 
heat  over  a  flame  to  boiling,  giving  the  fluid  a  rotary 
motion.  If  formaldehyde  is  present  a  blue  or  violet  color 
appears. 

Salicylic  Acid. — Salicylic  acid  is  not  often  used  to  pre- 
serve milk  because  it  is  not  very  soluble  in  that  fluid; 
0.04  per  cent,  will  prevent  milk  from  souring  for  36 
hours.  The  presence  of  salicylic  acid  may  be  detected 
by  the  following  test: 

Remonfs  Test. — Place  20  c.c.  of  milk  in  a  measuring 
cylinder  or  large  test  tube,  add  2  to  3  drops  of  sulphuric 
acid  and  20  c.c.  of  ether.  Mix  by  shaking  and  stand  aside 
until  the  ether  separates  and  forms  a  layer  at  the  top. 
The  fat  of  the  milk  and  any  salicylic  acid  present  is 
dissolved  by  the  ether.  The  ether  solution  is  drawn  off 
with  a  pipette,  placed  in  a  small  crucible  and  evaporated 
by  floating  the  crucible  in  hot  water.  The  residue  is 
rubbed  up  with  a  small  quantity  of  40  per  cent,  alcohol 
and  filtered  and  a  few  drops  of  ferric  chloride  solution 
are  added  to  the  filtrate.  A  violet  color  appears  if  salicy- 
lic acid  is  present. 

Benzole  Acid. — Like  salicylic  acid,  benzoic  acid  is  also 
not  very  soluble,  and  consequently  is  not  used  very  often 
to  preserve  milk.  The  various  tests  for  this  substance 
are  all  more  or  less  complicated. 

Peter's  test,  as  described  by  Leff mann,  is  as  follows : 
"  The  material  is  made  slightly  acid  and  extracted  with 


260        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

chloroform,  which  is  then  evaporated  spontaneously.  The 
vessel  containing  the  residue  is  placed  in  melting  ice,  2  c.c. 
of  sulphuric  acid  added,  and  stirred  until  the  residue  is 
dissolved.  Barium  dioxide  is  dusted  into  the  mass,  with 
constant  stirring,  until  the  liquid  begins  to  foam,  when 
3  c.c.  of  hydrogen  dioxide  (3  per  cent.)  are  added  drop 
by  drop.  The  dish  is  then  removed  from  the  cold  bath, 
the  contents  diluted  with  water  to  convenient  bulk,  and 
filtered.  The  acid  filtrate  is  extracted  with  chloroform. 
The  benzoic  acid  will  have  been  converted  into  salicylic 
acid  by  the  process  and  the  latter  may  be  detected  by 
dilute  solution  of  ferric  chloride  or  ammonio-ferric  sul- 
phate.'' 

Alkalies. — Alkalies  delay  the  curdling  of  milk  by 
neutralizing  the  acid  formed  by  bacteria.  The  substances 
which  have  been  used  for  this  purpose  are  the  carbonate 
and  bicarbonate  of  soda,  chalk,  and  potash.  When  mar- 
ket milk  gives  an  alkaline  reaction  to  litmus  or  has  a  low 
acidity,  as  determined  by  Mann's  test,  it  should  be  tested 
for  alkalies.  This  test  is  made  as  follows: 

Ten  c.c.  of  milk  are  mixed  in  a  test  tube  with  an 
equal  quantity  of  95  per  cent,  alcohol,  a  few  drops  of  a 
1  per  cent,  solution  of  rosolic  acid  are  added  and  mixed 
with  the  other  fluid  by  shaking.  If  an  alkali  is  present 
the  mixture  will  assume  a  rose-red  color.  If  no  alkali 
is  present  a  brownish-yellow  color  will  appear. 

STANDARD  METHODS  OF  COUNTING  BACTERIA1 

Collection  of  Samples. — The  milk  should  be  mixed 
thoroughly  before  the  sample  is  taken  and  not  less  than 
10  c.c.  should  be  collected  for  examination.  Bottled 

1  From  the  report  of  the  Laboratory  Section  of  the  Ameri- 
can Public  Health  Association,  Oct.  24,  1916. 


METHODS  OF  EXAMINING  MILK  261 

milk  may  be  mixed  by  inverting  the  bottle  several  times. 
If  the  milk  is  in  a  vessel  which  is  open  and  which  can- 
not therefore  be  inverted,  it  may  be  stirred  with  the 
pipette  which  is  used  to  transfer  the  sample  to  the  sample 
bottle.  The  pipette  should,  of  course,  be  sterile  and 
should  not  be  used  to  take  another  sample  until  it  has 
again  been  sterilized.  A  sterile  tube  with  straight  sides 
should  be  used  for  taking  a  sample  from  a  can.  An 
aluminum  tube  %  inch  in  diameter  and  21  inches  long 
is  most  convenient.  If  the  tube  is  held  vertically,  with 
the  opening  at  the  top  unobstructed,  and  is  inserted  into 
the  milk  slowly  until  the  lower  end  reaches  the  bottom  of 
the  can,  it  will  contain  a  column  of  milk  which  will  be 
representative  of  all  the  milk  in  the  can.  If  the  finger 
is  then  placed  firmly  upon  the  top  of  the  tube,  the  column 
of  milk  can  be  withdrawn  and  transferred  to  a  sterile 
sample  bottle,  which  should  be  large  enough  to  hold  the 
entire  contents  of  the  tube,  all  of  which  must  be  emptied 
into  the  bottle.  The  tube  must  be  washed  and  sterilized 
before  being  used  to  collect  a  sample  from  another  con- 
tainer. If  the  temperature  of  the  milk  is  to  be  taken,  a 
separate  sample  should  be  used  for  this  purpose  and  then 
discarded.  Glass-stoppered  bottles  or  those  provided 
with  cork-lined  screw  caps  are  the  most  satisfactory.  The 
bottle  containing  the  sample  should  be  properly  labelled 
and  immediately  placed  in  a  carrying  case  containing 
cracked  ice  so  that  the  milk  will  be  promptly  cooled  to 
near  the  freezing  point.  The  sample  bottles  should  be 
transferred  to  the  laboratory  as  soon  as  possible  and  the 
milk  plated  at  once.  If  the  plates  are  not  prepared  within 
four  hours  after  the  collection  of  the  samples  the  elapsed 
time  should  be  noted  in  the  report.  If  the  samples  are 


262         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

placed  in  iced-water  they  may  be  kept  for  twelve  hours 
without  an  increase  in  bacteria. 

All  apparatus  used  for  collecting,  measuring,  dilut- 
ing, and  plating  the  samples  must  be  sterilized  by  heat- 
ing at  a  temperature  of  at  least  175°  C.  for  one  hour. 

There  are  two  methods  of  counting  bacteria  in  milk: 
The  plate  method,  in  which  the  number  of  bacteria  per 
c.c.  of  milk  is  determined  by  counting  the  colonies  de- 
veloping on  agar  plates  to  which  a  measured  quantity 
of  milk  has  been  added;  and  the  direct  microscopic 
method,  in  which  a  small  measured  quantity  of  milk  is 
spread  over  a  definite  area  on  a  glass  slide,  dried,  fixed 
and  stained,  and  the  bacteria  counted  under  the  micro- 
scope. The  plate  method  is  the  oldest  and  best  under- 
stood and  is  recommended  for  general  purposes.  The 
microscopic  method  is  useful  when  rapid  results  are  de- 
sired, as  when  samples  are  examined  for  the  purpose  of 
classifying  or  grading  milk. 

PLATE  METHOD 

Medium. — The  medium  used  is  standard  beef  extract 
agar,  which  should  be  prepared  according  to  the  follow- 
ing directions: 

"  To  1000  c.c.  of  water  add  5  grammes  of  peptone 
and  3  grammes  of  beef  extract.  The  peptone  shall  be 
the  best  available,  and  the  beef  extract  shall  be  Liebig's 
where  this  is  obtainable.  Weigh  the  containing  dish  and 
its  contents. 

"  Dissolve  the  peptone  and  beef  extract  by  boiling 
and  replace  the  water  lost  through  evaporation. 

"  While  still  hot  filter  through  filter  paper. 

"  Add  12  grammes  of  oven-dried  agar,  or  15  grammes 
of  market  agar,  and  dissolve  by  boiling,  or  in  an  autoclav. 


METHODS  OF  EXAMINING  MILK  263 

Restore  the  weight  lost  by  evaporation.  It  is  imperative 
that  the  agar  be  of  the  best  quality  and  clean,  or  it  is 
impossible  to  obtain  a  clear  medium.  (When  an  auto- 
clav  is  at  hand  the  following  modification  is  convenient. 
Add  the  peptone  and  beef  extract  to  about  300  c.c.  of 
water,  and  the  agar  to  700  c.c.  Heat  both  in  an  autoclav 
under  15  Ibs.  pressure  one-quarter  hour.  Filter  the  broth 
while  hot  through  filtered  paper,  and  then  mix  the  broth 
with  the  melted  agar  and  filter  through  absorbent 
cotton. ) 

"  Determine  the  acidity  of  the  medium  by  titrating 
5  c.c.,  diluted  with  45  c.c.  water,  with  1/2o  normal  NaOH, 
phenolphthalein  being  used  as  an  indicator.  Any  at- 
tempt to  adjust  the  acidity  is  likely  to  make  undesirable 
changes  in  the  medium.  Inasmuch  as  variations  between 
+.5  and  +1.  acid  make  no  appreciable  difference  in  the 
results,  the  reaction  of  the  medium  is  not  to  be  changed 
if  it  falls  between  +  .5  and  +  .1  acid.  It  will  usually  be 
between  these  limits.  If  it  should  be  above  +  1.  acid,  add 
enough  normal  NaOH  to  bring  it  to  +  1.,  and  if  it  is 
below  +  .5  acid  add  enough  normal  HC1  to  bring  it  to 
+  .5,  always  adding  the  smallest  amount  of  the  reagent 
possible  to  bring  the  reaction  within  these  limits. 

"  Cool  to  45°  C.  and  then  heat  to  boiling  ( 15  minutes) 
and  filter  through  filter  paper  or  absorbent  cotton.  It 
is  necessary  that  the  filtering  be  continued  till  the  medium 
is  clear.  If  the  procedure  here  given  is  followed  and  a 
high  grade  of  agar  and  other  materials  is  used  there  will 
be  no  difficulty  in  getting  the  agar  clear.  Egg  should 
not  be  used  as  a  clarifier. 

"  After  filtering,  the  agar  may  be  either  tubed,  10 
c.c.  in  each  tube,  or  placed  in  flasks  containing  about  150 
c.c.  each.  The  latter  method  requires  less  glassware  and 


264        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

less  time,  and  is  found  to  be  equally  satisfactory  for 
plating,  as  explained  below. 

"  Sterilize  in  an  autoclav  at  15  Ibs.  pressure  (never 
above)  for  one-half  hour  after  dry  steam  comes  from  the 
autoclav.  As  an  alternative  the  medium  may  be  steri- 
lized on  three  successive  days  in  streaming  steam,  in 
which  it  must  remain  20  minutes  each  day  after  the  agar 
has  completely  melted. 

"  If  the  flasks  are  to  be  kept  for  more  than  a  couple 
of  days,  or  are  to  be  shipped,  before  using,  cover  the 
mouths  of  the  flasks  before  sterilizing  with  paper  fastened 
by  a  rubber  band  or  by  tinfoil  to  retard  evaporation." 

Dilutions. —  "For  miscellaneous  milk  samples  the 
character  of  which  is  not  known  three  dilutions  shall  be 
made:  1-100,  1-1000,  1-10,000.  Where  the  character 
of  the  milk  is  known  the  number  of  dilutions  may  be 
reduced.  If  the  milk  is  pasteurized,  certified,  or 
known  to  be  fresh  and  of  high  grade,  the  10,000 
and  1000  dilutions  may  be  omitted ;  if  the  milk  is  known 
to  be  old  and  of  high  bacterial  content  the  100  dilution 
may  be  omitted.  In  no  case  shall  less  than  two  plates 
be  made  of  each  sample. 

"  Any  convenient  method  of  making  dilutions  may 
be  used,  always  using  pipettes  and  sterile  water  blanks. 
The  water  used  for  dilutions  may  be  placed  in  dilution 
bottles  (99  c.c.  and  9  c.c.  are  convenient  sizes)  and 
sterilized  for  one  hour  in  an  autoclav  at  15  Ibs.  pressure. 
These  should  be  marked  so  that  it  can  be  determined  that 
they  have  neither  gained  nor  lost  water  during  or  subse- 
quent to  sterilization.  Or  the  water  may  be  sterilized 
in  bulk,  if  kept  in  a  properly  guarded  container,  and 
subsequently  measured  directly  into  dilution  bottles  with 
sterilized  pipettes. 


METHODS  OF  EXAMINING  MILK  265 

"  The  dilution  bottles  should  have  glass  stoppers  or 
some  other  type  of  closing  that  makes  shaking  possible. 
Cotton  plugs  are  unsatisfactory  because  the  dilution 
water  will  soak  into  the  cotton. 

"  Straight-sided  pipettes  graduated  to  deliver  be- 
tween two  marks  are  best,  but  pipettes  marked  to  deliver 
may  be  used  if  care  is  taken  that  the  points  are  not  broken, 
and  the  tube  is  completely  emptied. 

"  In  making  dilutions  the  original  sample  and  each 
dilution  bottle  shall  be  shaken  25  times,  each  shake  being 
an  up-and-down  motion  with  an  excursion  of  about  one 
foot.  After  the  final  dilution  fill  a  pipette  to  the  mark 
and  allow  the  contents  to  run  into  an  empty  Petri  dish, 
the  end  of  the  pipette  touching  the  bottom  of  the  dish 
as  the  liquid  runs  out.  If  the  pipette  is  one  that  delivers 
1  c.c.,  be  sure  that  the  last  drop  is  carried  into  the  Petri 
dish.  (Pipettes  should  be  placed  immediately  in  water 
after  using  to  make  subsequent  cleaning  easier.) " 

Mating. — "  The  agar  in  the  flasks  (or  test  tubes) 
shall  be  melted  in  boiling  water  or  steam  and  after 
melting  should  be  cooled  to  45°  C.  before  using. 

"  Pour  10  c.c.  of  the  melted  agar  in  each  inoculated 
Petri  dish,  and  by  a  gentle  rotary  motion  thoroughly  mix 
the  agar  and  the  diluted  milk.  As  nearly  as  possible  the 
same  amount  of  agar  should  be  poured  into  each  Petri 
dish  so  that  the  depth  of  the  agar  in  all  be  uniform.  If 
desired,  10  c.c.  may  be  measured  out  from  the  flask  with 
a  sterile  pipette. 

"  After  dilution  of  the  milk  not  more  than  half  an 
hour  should  elapse  before  the  agar  is  poured  into  the 
Petri  dishes. 

"  After  the  agar  has  thoroughly  hardened  place  the 
Petri  dishes  in  an  incubating  oven,  inverted,  in  order  to 


266         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

reduce  the  danger  of  spreaders.  While  clay  tops  of 
Petri  dishes  are  useful  for  some  purposes  they  are  not 
recognized  in  the  standard  methods." 

Incubation. — "  Only  one  period  of  incubation  and 
one  temperature  is  regarded  as  standard,  48  hours  at 
37.5°  C.  In  crowded  incubators  ventilation  should  be 
provided." 

Counting. — "  If,  among  the  different  dilutions,  there 
are  plates  containing  from  30  to  300  colonies  these  should 
be  counted,  and  the  number,  multiplied  by  the  dilution, 
be  reported  as  the  final  count.  All  colonies  on  such 
plates  should  be  counted  and  the  numbers  averaged.  If 
there  are  no  plates  within  these  limits  the  one  that  comes 
nearest  to  300  is  to  be  counted.  No  plate  that  contains 
less  than  twenty  colonies  shall  be  counted,  unless  it  hap- 
pens that  there  are  no  plates  with  a  larger  number  of 
colonies,  or  unless  the  numbers  in  the  plates  check  with 
other  dilutions.  If  the  number  of  colonies  on  the  plate 
to  be  counted  is  over  300,  a  part  of  the  plate  may  be 
counted,  and  the  whole  plate  averaged. 

"  Counting  shall  be  done  with  a  lens,  magnifying 
2%  diameters  (or  what  the  opticians  call  a  3%  +  lens). 
Nearsighted  persons  should  use  their  glasses  in  counting, 
but  farsighted  persons  should  remove  them.  In  case  it 
is  doubtful  whether  certain  objects  are  colonies  or  dirt 
specks  they  should  be  examined  with  a  compound  micro- 
scope." 

Reports. — "  In  making  reports  it  must  be  borne  in 
mind  that  with  high  numbers  obtained  by  the  routine 
method  only  an  approximation  to  accuracy  can  be  ob- 
tained. Only  the  left-hand  figures  of  the  final  numbers 
are  of  significance.  It  is  best,  therefore,  to  report  only 
the  two  left-hand  figures  of  the  results  in  order  to  avoid 


METHODS  OF  EXAMINING  MILK  267 

an  unwarranted  impression  of  accuracy.  For  example, 
when  the  numbers  are  in  millions  no  figures  smaller  than 
the  millions  have  any  significance  in  the  routine  analysis 
of  milk.  In  making  the  report  raise  the  number  to  the 
next  highest  round  number,  but  never  lower  it. 

"  In  no  case  shall  the  count  of  a  single  plate  be  re- 
garded as  sufficient  for  the  purpose  of  grading  milk.  If 
a  single  sample  of  milk  only  is  to  be  tested  there  should 
be  at  least  three  plates  counted  before  a  report  is  made." 

MICROSCOPIC  METHOD 

The  apparatus  required  for  this  method  consists  of 
a  microscope,  a  supply  of  ordinary  glass  slides,  and  a 
straight  capillary  pipette  marked  to  deliver  1/100  c.c., 
with  the  graduation  mark  1%  to  2%  inches  from  the  tip. 
The  calibration  should  be  tested  by  weighing  on  chemical 
balances  the  quantity  of  milk  delivered  when  the  pipette 
is  filled  to  the  mark.  One  pipette  may  be  used  for  a  num- 
ber of  samples  of  milk  provided  it  is  kept  clean.  This 
may  be  done  by  rinsing  the  interior  with  clean  water 
after  each  sample  and  wiping  the  exterior  with  a  clean 
towel. 

Preparation  of  Smears. — "  One  one-hundredth  c.c. 
of  milk  or  cream  is  deposited  upon  a  clean  glass  slide  by 
means  of  the  pipette  above  described.  By  the  use  of  a 
clean  stiff  needle  this  drop  of  milk  is  spread  over  an 
area  of  one  square  centimetre.  This  may  be  most  con- 
veniently done  by  placing  the  slide  upon  any  glass  or 
paper  ruled  into  areas  one  centimetre  square.  These 
marks  showing  through  the  glass  serve  as  guides.  After 
uniform  spreading  the  preparation  is  dried  in  a  warm 
place  upon  a  level  surface.  In  order  to  prevent  notice- 
able growth  this  drying  must  be  accomplished  within 


268        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

five  to  ten  minutes ;  but  excessive  heat  must  be  avoided 
or  the  dry  films  may  crack  and  peel  from  the  slides  in  later 
handling. 

"  After  drying  the  slides  are  to  be  dipped  in  xylol 
(gasoline  may  be  used)  for  one  minute,  then  drained 
and  the  slides  dried.  They  are  then  immersed  in  90  per 
cent,  grain  or  denatured  alcohol  for  one  minute  or  more 
and  then  transferred  to  a  fresh  aqueous  solution  of  methy- 
lene  blue.  Old  or  unfiltered  stains  are  to  be  avoided,  as 
they  may  contain  troublesome  precipitates.  The  slides 
remain  in  this  solution  from  five  seconds  to  one  minute 
or  longer,  depending  upon  the  effect  desired,  and  are  then 
rinsed  in  water  to  remove  the  surplus  stain,  and  decolor- 
ized in  alcohol.  The  decolorization  takes  several  seconds 
to  a  minute,  during  which  time  the  slides  must  be  under 
observation  in  order  that  the  decolorization  may  not  pro- 
ceed too  far  before  they  are  removed  from  the  alcohol. 
When  properly  decolorized  the  general  background  of 
the  film  should  show  a  faint  blue  tint.  Poorly  stained 
slides  may  be  decolorized  and  restained  as  many  times  as 
necessary  without  any  apparent  injury.  After  drying, 
the  slides  may  be  examined  at  once,  or  they  may  be  filed 
away  and  preserved  for  further  reference." 

Standardization  of  the  Microscope. — "  The  micro- 
scope to  be  used  must  be  adjusted  in  such  a  way  that 
each  field  of  the  microscope  covers  a  certain  known  frac- 
tion of  the  total  square  centimetre's  area.  This  pro- 
cedure is  simple  with  the  proper  materials  at  hand.  The 
microscope  should  have  a  1.9  mm.  (Vi2  inch)  oil  immer- 
sion objective,  and  an  ocular  giving  approximately  the 
field  desired,  and  should  preferably  be  fitted  with  a 
mechanical  stage.  To  standardize  the  microscope,  place 
upon  the  stage  a  stage  micrometer,  and  by  the  selection 


METHODS  OF  EXAMINING  MILK  269 

of  oculars  or  adjusting  the  draw  tube,  or  both,  bring  the 
diameter  of  the  whole  microscopic  field  to  .205  mm. 
When  so  adjusted  the  microscopic  field  will  cover  almost 
exactly  1/300,000  of  a  cubic  centimetre  of  the  milk 
(actually  1/302840).  This  means  that  if  the  bacteria 
in  one  field  only  are  counted  the  number  should  be 
multiplied  by  300,000  to  give  the  total  number  in  a  cubic 
centimetre.  If  the  bacteria  in  a  hundred  fields  are  to 
be  counted  the  total  should  of  course  be  multiplied  by 
3000. 

"  Inasmuch  as  it  is  difficult  to  count  bacteria  lying 
near  the  margin  of  the  microscopic  field,  it  is  much  better 
to  have  an  eyepiece  micrometer  with  a  circular  ruling 
8  mm.  in  diameter  and  divided  into  quadrants.  This 
will  give,  in  the  microscopic  field,  a  smaller  area  within 
which  the  bacteria  may  be  seen  most  sharply,  and  which 
may  be  more  easily  counted.  Such  eyepiece  micrometers 
are  now  manufactured  by  laboratory  supply  houses  and 
may  be  easily  obtained.  In  the  use  of  this  eyepiece 
micrometer  the  inner  circle,  by  the  adjustment  of  the 
draw  tube,  should  be  made  to  cover  a  circle  with  a  diam- 
eter of  .146  mm.  In  this  case  this  inner  circle  will  cover 
1/600,000  of  a  cubic  centimetre  of  milk,  meaning,  of 
course,  that  the  number  of  bacteria  in  a  single  field  should 
be  multiplied  by  600,000,  or,  if  a  hundred  fields  are 
counted,  by  6000,  to  obtain  the  number  per  cubic  centi- 
metre. 

"  The  number  of  microscopic  fields  to  be  counted  will 
depend  somewhat  upon  the  kind  of  data  that  is  desired. 
If  this  method  is  to  be  used  simply  for  the  purpose  of 
dividing  milk  into  grades,  it  will  in  most  cases  be  un- 
necessary to  do  the  actual  counting,  since  a  Grade  A 
milk  will  show  field  after  field  without  any  bacteria  at 


270        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

all,  while  a  Grade  C  milk  will  show  the  field  crowded  with 
bacteria.  In  all  doubtful  cases,  however,  counting  should 
be  done,  and  there  should  never  be  less  than  thirty  fields 
counted  in  order  to  have  reliable  results.  Counting  thirty 
fields  is  not  so  tedious  a  task  as  it  would  seem  to  be,  since 
in  ordinary  milk  the  number  of  bacteria  in  each  field  is 
small,  and  the  counting  may  be  done  very  rapidly." 

Counting. — "  Counting  the  bacteria  in  such  a  smear 
may  be  done  in  two  ways:  1.  The  number  of  groups  of 
one  or  more  bacteria  present.  2.  The  number  of  indi- 
viduals. The  second,  of  course,  is  really  the  correct  count 
of  the  number  of  bacteria,  but  the  former  will  give  a 
count  much  closer  to  that  obtained  by  the  plate  count, 
since  the  colonies  upon  the  plate  represent  groups  of  bac- 
teria rather  than  individuals,  each  group  growing  into 
a  single  colony  only.  Extensive  tests  have  shown  that 
there  is  a  fair  correspondence  between  the  number  of 
groups  reported  by  experienced  observers  and  the  num- 
ber of  colonies  that  may  grow  in  plates  made  from  the 
same  milk,  although  there  are  occasionally  discrepancies 
of  considerable  extent.  These  discrepancies  are  caused 
by  variations  in  judgment  as  to  what  constitutes  a 
group,  variations  in  the  extent  to  which  groups  break 
up  in  the  dilution  waters  when  the  smears  are  made, 
and  the  presence  of  dead  bacteria  or  of  bacteria  which  do 
not  grow  on  the  plates.  Some  experience  is  needed  by 
the  microscopist  in  determining  just  what  should  be 
counted.  In  high-grade  milks  an  inexperienced  person 
is  apt  to  fail  to  recognize  differences  between  bacteria 
and  other  minute  objects.  This  results  as  a  rule  in  an 
overcount  by  inexperienced  men.  In  milk  containing 
many  readily  recognizable  bacteria  in  each  field  the  in- 


METHODS  OF  EXAMINING  MILK  271 

experienced  man  is  apt  to  overlook  some  of  them,  giving 
an  undercount.  These  difficulties  are  overcome,  how- 
ever, by  training  and  experience. 

COMPARISON  OF  RESULTS  OBTAINED  BY  THE  TWO  METHODS 

"  It  must  be  recognized  that  the  results  obtained  from 
the  microscopic  record  give  a  closer  approximation  to 
the  actual  number  of  bacteria  present  in  the  milk  than 
those  obtained  by  the  plate  method,  since  the  plate 
method  will  count  as  one  either  a  single  bacterium  or  a 
group  which  may  sometimes  contain  a  hundred  or  even 
more  individuals.  Inasmuch,  however,  as  the  plate  count 
has  become  a  method  of  analysis  that  is  well  known  and 
commonly  applied,  it  becomes  desirable  to  know  as  closely 
as  possible  what  relations  there  may  be  between  the  plate 
count  and  the  microscopic  count.  Experience  has  shown 
that  the  count  of  individual  bacteria  is  ordinarily  1.5  to  8 
times  as  great  as  the  plate  count,  the  ratio  between  the 
two  being  largely  dependent  upon  the  size  of  the  clumps 
of  bacteria  present.  Where  the  bacteria  are  mostly  iso- 
lated, the  ratio  of  the  two  counts  would  be  much  closer 
than  where  there  are  present  long  chains  of  streptococci 
or  masses  of  cocci.  After  one  has  had  a  little  experience 
in  counting  clumps  it  is  found  that  the  number  of  groups 
shown  by  the  microscope  agrees  fairly  well  with  the  num- 
ber of  colonies  shown  by  the  plate  count,  though  even  here 
there  are  occasionally  discrepancies,  due  among  other 
things  to  the  appearance  in  the  microscope  of  kinds  of 
bacteria  which  fail  to  grow  in  the  culture  media  used  in 
making  plates.  In  all  cases,  however,  the  direct  count  of 
raw  milk  will  give  a  much  closer  approximation  to  the 
actual  numbers  of  bacteria  than  the  plate  count.  In  view 
of  these  facts  it  is  difficult  to  interpret  one  count  in  terms 


272        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

of  the  other ;  but  a  few  suggestions  will  give  a  fairly  sat- 
isfactory idea  as  to  how  the  two  may  be  related. 

"Grade  A  raw  milk,  which  should  have  less  than  100,- 
000  bacteria  per  c.c.,  will  not  show  more  than  three  to  four 
small  clumps  of  bacteria  for  each  30  fields  of  the  micro- 
scope where  the  diameter  of  the  fields  is  .205  mm.  Such 
milk  also  ought  not  to  contain  more  than  500,000  individ- 
ual bacteria  per  c.c.  when  counted  by  the  microscope. 
For  Grade  A  pasteurized  milk  (which  should  have  less 
than  200,000  per  c.c.  by  the  plate  count  before  pasteuri- 
zation) the  microscope  should  not  show  more  than  six  to 
eight  clumps  per  30  microscopic  fields,  and  not  more  than 
1,000,000  individual  bacteria  when  counted  with  the 
microscope. 

"Grade  B  milk,  which  is  supposed  not  to  have  more 
than  1,000,000  bacteria  before  pasteurization,  when 
counted  by  the  plating  method,  should  not  show  more 
than  20  individual  bacteria  per  field,  where  the  diameter 
of  the  fields  is  .205  mm.,  and  not  more  than  three  to  four 
groups  of  bacteria  per  field. 

"While  the  above  relation  between  the  plate  count 
and  the  microscopic  counts  cannot  be  relied  upon  as  hav- 
ing a  very  great  amount  of  accuracy,  it  will  serve  to  give 
a  general  idea  of  the  ratio  between  the  two  under  or- 
dinary conditions,  and  may  serve  as  a  guide  in  the  use  of 
the  direct  microscopic  method." 

EXAMINATION  FOR  STREPTOCOCCI 

When  long-chain  streptococci  are  found  in  milk  sedi- 
ment in  association  with  an  excess  of  leucocytes  and  the 
latter  cells  are  clumped  together  and  consist  largely  of 
the  polymorphonuclear  type,  there  need  be  no  hesitancy 
in  concluding  that  the  streptococci  are  pathogenic  and 


METHODS  OF  EXAMINING  MILK  273 

that  the  milk  under  examination  contains  the  secretion  of 
a  cow  affected  with  catarrhal  mastitis. 

If  the  plates  prepared  from  a  sample  of  herd  milk 
contain  a  large  number  of  extremely  minute  brownish 
colonies,  which  upon  microscopic  examination  are  found 
to  consist  of  streptococci  in  rather  long  chains,  an  ex- 
amination of  the  herd  from  which  the  milk  came  will  re- 
sult in  the  discovery  of  one  or  more  cows  affected  with 
catarrhal  mastitis.  To  examine  microscopically,  place  one 
of  the  colonies  in  a  drop  of  water  on  a  glass  slide  and 
spread  by  a  gentle  rotary  motion  of  the  platinum  nee- 
dle, beginning  at  the  centre  and  working  outward;  dry, 
fix  by  heat  and  stain  with  methylene  blue.  The  chains 
of  Streptococcus  lacticus  are  shorter  than  those  of  the 
streptococci  of  mastitis,  rarely  containing  more  than  6  or 
8  cocci,  and  the  individual  cocci  are  arranged  as  diplo- 
cocci.  (See  Figs.  5  and  6.) 

The  method  of  examination  for  streptococci  recom- 
mended by  the  Laboratory  Section  of  the  American 
Public  Health  Association  is  as  follows : 

"  Where  streptococci,  diplococci,  or  cocci  are  found  in 
the  sediment,  and  the  plate  from  the  same  sample  con- 
tains colonies  resembling  streptococci  colonies,  these  colo- 
nies may  be  grown  in  bouillon  to  see  if  chains  will  develop. 

"First  make  and  record  an  estimate  of  the  number  of 
such  colonies  present,  then  transfer  from  10  to  50  of  them 
to  bouillon  and  grow  for  15  to  24  hours  at  37°  C.  To  ex- 
amine the  bouillon  culture,  spread  a  loopful  on  a  glass 
slide,  fix  with  heat,  fix  with  alcohol  while  slide  is  still  quite 
hot,  stain  with  methylene  blue,  wash  immediately,  dry 
and  examine. 

"A  milk  should  not  be  condemned  because  a  few 
chains  are  found  together  with  large  numbers  of  other 
18 


274        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

microscopic  organisms  in  a  bouillon  culture,  but  it  is  safer 
to  exclude  a  milk  from  the  market  when  these  three  tests 
agree: 

"1.  Microscopic  examination  of  the  sediment  shows 
streptococci,  diplococci,  or  cocci. 

"2.  The  plate  from  the  same  sample  shows  colonies 
resembling  streptococci  colonies  exceeding  a  count  of 
100,000  to  a  cubic  centimetre. 

"3.  The  bouillon  culture  from  these  colonies  shows 
long-chain  streptococci  alone  or  in  great  excess  compared 
with  the  other  bacteria  present. 

"Milk  showing  in  the  stained  sediment  both  abund- 
ance of  long-chain  streptococci  and  pus  should  be  con- 
demned as  unsafe." 

The  bouillon  used  in  this  examination  may  be  pre- 
pared as  follows : 

"Infuse  500  g.  finely  chopped  lean  meat  24  hours 
with  1,000  c.c.  distilled  water  in  refrigerator;  restore  loss 
by  evaporation;  strain  infusion  through  cotton  flannel." 
(Or,  dissolve  5  g.  of  beef  extract,  preferably  Liebig's, 
in  1,000  c.c.  distilled  water.) 

"  Add  1  per  cent,  peptone.  Warm  on  water  bath, 
stirring  until  peptone  is  dissolved. 

"  Heat  over  boiling  water  or  steam  bath  thirty  min- 
utes. Restore  loss  by  evaporation. 

"Titrate,  adjust  reaction  to  +  1  per  cent,  by  adding 
normal  sodium  hydrate. 

"Boil  two  minutes  over  a  free  flame,  constantly  stir- 
ring. Restore  loss  by  evaporation. 

"Filter  through  absorbent  cotton,  passing  the  liquid 
through  until  clear.  Titrate  and  record  final  reaction. 
Tube,  using  10  c.c.  to  each  tube.  Sterilize." 


METHODS  OF  EXAMINING  MILK  275 

EXAMINATION  FOR  COLI 

The  presumptive  tests  for  Bacillus  coli  do  not  have 
the  same  value  in  milk  examination  as  in  water  analysis, 
because  it  is  practically  impossible  to  obtain  milk  from 
the  cow,  even  under  good  dairy  conditions,  without  it 
being  infected  to  some  extent  with  colon  bacilli  from  the 
intestines  of  the  animal.  The  detection  of  this  organism 
in  milk  is  therefore  of  little  value,  except  that  when  it  is 
present  in  large  numbers  it  is  an  evidence  of  uncleanli- 
ness  and  usually  an  indication  of  gross  fecal  contamina- 
tion. 

One  of  the  presumptive  tests  for  Bacillus  coli  in  milk 
approved  by  the  Laboratory  Section  of  the  American 
Public  Health  Association  is  made  as  follows:  "1  c.c.  of 
a  1  to  1,000  dilution  of  milk  is  placed  in  ordinary  bile 
containing  1  per  cent,  lactose  in  a  fermentation  tube  and 
allowed  to  stand  at  37°  C.  for  72  hours,  at  the  end  of 
which  time,  if  there  is  more  than  15  per  cent,  gas,  plates 
are  made,  colonies  isolated  and  run  through  species  tests." 

The  fermentation  test  described  on  page  278  is  a 
simple  and  convenient  method  of  detecting  the  presence 
of  an  excessive  number  of  coli  or  other  gas-forming  or- 
ganisms in  milk. 

EXAMINATION  FOR  TUBERCLE  BACILLI 

The  method  recommended  by  the  Laboratory  Section 
of  the  American  Public  Health  Association  is  as  follows : 

"Pint  or  quart  samples  of  milk  should  be  obtained, 
kept  well  iced,  and  delivered  to  the  laboratory  as  soon  as 
possible.  The  milk  and  cream  should  be  well  mixed  by 
shaking  vigorously.  50  c.c.  of  the  mixed  milk  are  then 
transferred  to  a  large  centrifuge  flask  and  100  c.c.  of 
sterile  water  added.  Centrifuge  for  one  hour  at  2,000 


276         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

revolutions  per  minute.  The  milk  is  diluted  with  twice 
its  volume  of  water  with  the  idea  that  it  will  decrease  the 
specific  gravity  of  the  milk  and  so  permit  of  the  easier 
sedimentation  of  the  tubercle  bacilli.  Guinea  pigs  are 
then  inoculated,  subcutaneously  in  the  belly  wall,  with  5 
c.c.  of  the  sediment  thus  obtained.  The  guinea  pigs  not 
dying  in  at  least  two  months  are  chloroformed,  after 
being  tested  with  tuberculin,  and  careful  autopsies  made. 
Smears,  cultures  and  sections  are  made  from  the  various 
organs  of  the  animals  that  show  any  change  from  the  nor- 
mal. The  smears  are  stained  with  carbol  fuchsin  and  ex- 
amined for  acid- fast  bacilli. 

"  Cultures  are  made  on  glycerinized  potato  and  glyc- 
erine agar  to  rule  out  Rabinowitch's  quick  growing  acid- 
fast  butter  bacillus. 

"Sections  are  stained  with  carbol  fuchsin  for  tubercle 
bacilli  and  also  with  haematin  and  eosin  for  histological 
appearances. 

"Tuberculous  guinea  pigs  may  be  differentiated  from 
nontuberculous  by  giving  sufficient  crude  tuberculin  (2 
c.c.)  subcutaneously  to  cause  the  death  of  the  tuberculous 
animals  in  twenty- four  hours. 

"It  is  of  course  understood  that  the  examination  of 
milk  for  tubercle  bacilli  is  by  the  very  nature  of  the  test 
limited.  For  the  control  of  this  disease  in  cattle  we  must 
rely  upon  the  tuberculin  test." 

MicroscopicMethod — Some  of  the  sediment  obtained  by 
centrif ugalizing  the  milk  is  spread  thinly  on  a  glass  slide, 
fixed  by  heating,  stained  with  carbol  fuchsin,  decolorized 
in  acid  alcohol  and  counter-stained  with  methylene  blue. 
If  small  flakes  or  clots  are  present  in  the  milk,  one  of 
these  is  spread  on  the  slide  and  treated  in  the  same  man- 
ner. The  carbol-fuchsin  solution  is  prepared  by  dissolv- 


METHODS  OF  EXAMINING  MILK  277 

ing  1  gramme  of  fuchsin  in  10  c.c.  of  alcohol  and  100  c.c. 
of  a  5  per  cent,  solution  of  phenol  in  water,  and  then 
filtering  the  solution.  The  acid  alcohol  is  prepared  by 
mixing  5  c.c.  of  nitric  or  one  of  the  other  mineral  acids 
with  95  c.c.  of  alcohol.  After  the  smear  on  the  slide  has 
been  fixed,  it  is  flooded  with  carbol  fuchsin  and  the  slide 
is  held  over  a  Bunsen  flame  and  the  stain  kept  steaming 
for  3  minutes.  The  slide  is  then  rinsed  with  water  and 
the  preparation  treated  with  the  acid  alcohol  until  the 
red  color  disappears.  Next,  the  acid  alcohol  is  rinsed  off 
with  water  and  the  preparation  is  stained  for  3  minutes 
with  methylene  blue,  after  which  the  slide  is  washed  with 
water,  dried,  and  examined  with  the  1/12  oil  immersion 
objective.  Any  tubercle  bacilli  present  will  be  stained 
red;  other  organisms  will  be  stained  blue.  While  the 
presence  of  tubercle  bacilli  may  be  accepted  as  proof  that 
the  cow  from  which  the  milk  came  is  infected  with  tuber- 
culosis, failure  to  find  these  organisms  cannot  be  re- 
garded as  positive  evidence  that  the  animal  is  not  tuber- 
culous. Tubercle  bacilli  may  be  present  in  small  numbers 
and  escape  detection  on  microscopic  examination.  The 
so-called  acid-fast  organisms  are  also  stained  red  by  car- 
bol fuchsin.  They  may  be  present  in  milk  and  butter,  but, 
apparently,  they  usually  enter  the  milk  after  it  is  drawn 
from  the  udder.  Jensen  is  of  the  opinion  that  if  precau- 
tions are  taken  to  prevent  contamination  of  the  milk 
sample  when  it  is  drawn  from  the  udder,  these  organisms 
will  very  rarely  cause  errors  in  diagnosis. 

Antif  or min  Method. — Take  5  c.c.  of  the  milk  to  be  ex- 
amined and  mix  it  with  5  c.c.  of  absolute  alcohol,  5  c.c. 
of  ether,  10  c.c.  of  a  25  per  cent,  solution  of  antiformin 
and  25  c.c.  of  normal  saline  solution.  Place  in  an  incu- 


278        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

bator  for  at  least  one-half  hour.  Centrif ugalize,  prepare 
a  slide  from  the  sediment,  and  stain  as  described  for  the 
microscopic  method. 

FERMENTATION  TEST 

The  fermentation  test  has  been  in  use  in  cheese  fac- 
tories for  a  long  time  to  detect  milk  which  is  unsuitable 
for  cheese-making.  It  can  be  used  in  milk  control  work 
to  discover  the  presence  of  the  more  objectionable  milk 
bacteria,  such  as  the  gas-formers  and  peptonizers,  and 
thus  ascertain  what  form  of  decomposition  the  milk  is 
likely  to  undergo  with  age,  especially  if  improperly  cared 
for.  It  is  also  of  assistance  in  determining  the  source  of 
excessive  bacterial  contamination. 

The  test  is  very  simple  and  does  not  require  any  spe- 
cial apparatus.  In  cheese  factories,  bottles  holding  from 
120  to  140  c.c.  or  test  tubes  of  40  to  50  c.c.  capacity  are 
used  for  the  milk  samples.  After  the  milk  is  introduced, 
they  are  closed  with  a  rubber  stopper  and  are  held  at  a 
temperature  of  37  to  38°  C.  in  a  water  bath.  In  a  labora- 
tory, it  is  more  convenient  to  use  the  test  tubes  ordinarily 
used  for  bacteriological  cultures  and  to  place  the  tubes 
in  an  incubator  after  the  milk  has  been  placed  in  them. 

The  test  tubes  are  washed  and  cleansed  in  the  usual 
manner,  plugged  with  cotton  and  sterilized  by  heating  in 
a  hot-air  sterilizer  for  2%  hours  at  150  to  160°  C.  It  is 
important  that  the  tubes  be  sterilized,  since  any  organ- 
isms in  the  tubes  will  develop  in  the  milk  and  may  influ- 
ence the  result.  Each  tube  is  numbered  with  a  paraffine 
pencil  to  correspond  with  the  sample  of  milk  and  is  then 
filled  with  milk  to  within  a  finger's  breadth  of  the  bottom 
of  the  cotton  plug,  closed  with  the  cotton  plug  and  placed 
in  the  incubator.  In  transferring  the  milk  from  the  ves- 


METHODS  OF  EXAMINING  MILK  279 

sel  in  which  it  was  collected  to  the  test  tube,  the  necessary 
precautions  should  be  observed  to  prevent  contamination. 
Twelve  hours  after  they  are  placed  in  the  incubator, 
the  samples  are  examined.  If  the  milk  is  normal,  fresh 
and  of  good  quality,  there  will  be  no  change  apparent  ex- 
cept perhaps  a  clean,  sour  odor.  The  beginning  of  fer- 
mentation or  curdling  is  indicated  by  an  upward  bulging 
of  the  cream  layer  and  the  presence  of  a  greenish  layer 
beneath  it.  If  there  is  no  change  at  this  time,  the  samples 
are  to  be  replaced  in  the  incubator  and  observed  again  in 
twelve  hours,  and  subsequently  at  twelve-hour  periods  if 
necessary.  If  curdling  does  not  take  place  after  forty- 
eight  hours,  the  reaction  of  the  milk  should  be  taken  and 
tests  made  for  preservatives.  When  the  milk  curdles,  the 
time  of  curdling  and  the  character  of  the  curd  are  to  be 
noted.  The  time  of  curdling  depends  upon  the  number  of 
bacteria  present  which  are  not  inert,  while  the  character 
of  the  curd  depends  upon  the  kind  of  bacteria  which  pre- 
dominate. The  types  of  curds,  the  symbols  by  which  they 
are  recorded,  and  their  indications  are  as  follows: 

1.  Jelly-like  Curd. — Ji,  solid,  smooth,  white,  jelly- 
like  curd,  with  no  fluid.  J2,  curd  of  same  type,  but  show- 
ing a  few  furrows  or  gas  bubbles.  J3,  curd  same,  but 
showing  more  furrows  and  gas  bubbles  and  also  cracks, 
with  some  fluid.  The  jelly-like  curd  is  produced  when 
the  acid- forming  bacteria  predominate,  and  if  the  number 
of  bacteria  is  excessive  it  usually  indicates  that  the  milk 
vessels  or  utensils  are  unclean,  or  that  the  milk  is  old  or 
has  not  been  kept  under  proper  conditions. 

2.  Peptowzed  Curd. — The  curd  may  be  firm,  jelly- 
like,  with  ragged  surfaces,  or  it  may  be  soft,  flocculent 
or  "mushy,"  associated  in  either  case  with  more  or  less 
fluid.  Pi,  the  amount  of  fluid  is  small  in  proportion  to 


280        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

the  size  of  the  curd.  P2,  increased  amount  of  fluid,  less 
curd.  P3,  amount  of  fluid  large  in  proportion  to  the  size 
of  the  curd.  This  type  of  curd  is  produced  when  a  large 
proportion  of  peptonizing  bacteria  are  present  in  the 
milk.  When  the  number  of  bacteria  is  large,  it  is  usually 
an  indication  that  the  milk  has  been  contaminated  with 
dust  from  hay,  fodder  or  soil,  or  that  a  suppurative  con- 
dition is  present  in  the  herd.  When  milk  is  produced 
under  good  conditions  and  is  kept  cool,  the  peptonizing 
bacteria  (udder  cocci)  will  predominate  but  the  total 
number  of  bacteria  will  be  small. 

3.  Gaseous  Curd. — A  white,  jelly-like  curd  contain- 
ing gas  bubbles  and,  when  gas  has  been  formed  in  large 
quantity,  presenting  a  sponge-like  appearance.     More 
or  less  fluid  is  present  and  this  may  also  contain  gas  bub- 
bles.   Gi,  a  few  gas  bubbles  in  the  cream  layer  or  in  the 
curd.    G2,  gas  bubbles  numerous  in  the  cream  and  curd ; 
gas  bubbles  may  also  be  present  in  the  fluid.    G3,  curd 
sponge-like,  containing  many  gas  bubbles ;  may  be  split 
and  a  portion  driven  to  the  top;  gas  bubbles  in  fluid. 
The  gaseous  curd  is  produced  when  a  large  percentage 
of  gas-forming  bacteria  is  present  and  is  usually  an  in- 
dication that  the  milk  has  been  contaminated  with  an  ex- 
cessive amount  of  manure.    It  may  also  occur  when  pol- 
luted water  is  used  to  wash  the  milk  vessels  and  utensils. 

4.  "Flaky"  or  Flocculent  Curd. — Curd  in  flakes  or 
flocculi,  associated  with  a  turbid  fluid,  which  may  be 
whitish,  yellowish,  or  otherwise  discolored.    Fli,  curd  in 
fine  flakes  or  partially  homogeneous.    F12,  large  flakes 
and  considerable  fluid.    F13,  large  flakes,  torn,  with  white 
or  discolored  fluid.    This  type  of  curd  is  produced  when 
saccharomyces  which  ferment  lactose  are  present  in  large 
numbers.    The  casein  is  permeated  with  fine  gas  bubbles 


METHODS  OF  EXAMINING  MILK  281 

at  the  moment  of  precipitation,  which  causes  it  to  be 
broken  up  into  flakes;  the  fluid  is  turbid  because  of  the 
movement  produced  by  the  gas  developed  (O.  Jensen). 

ESTIMATION  OF  THE  NUMBER  OF  LEUCOCYTES 

There  are  a  number  of  methods  for  determining  the 
leucocyte  content  of  milk,  each  having  a  different  limit 
for  normal  milk.  In  several,  the  milk  is  centrif ugalized, 
a  portion  of  the  sediment  is  spread  on  a  glass  slide,  fixed, 
and  stained,  and  the  number  of  leucocytes  in  the  field  of 
the  1/12  oil  immersion  objective  is  counted.  In  others, 
the  leucocytes  in  a  measured  volume  of  sediment  or  milk 
are  counted  or  the  quantity  of  sediment  in  a  definite  vol- 
ume of  milk  is  measured.  Of  these  methods,  those  most 
commonly  used  are  the  following: 

Stokes'  Test. — 10  c.c.  of  milk  is  placed  in  a  sediment 
tube  and  centrifugalized  for  10  minutes,  after  which  the 
cream  and  separated  milk  are  poured  off.  A  platinum 
loopful  of  the  sediment  is  spread  on  a  glass  slide  over  an 
area  of  1  square  centimetre,  dried  in  the  air,  fixed  in  the 
flame,  and  stained  with  methylene  blue  for  2  or  3  minutes. 
The  specimen  is  then  placed  under  the  microscope  and 
examined  with  the  1/12  oil  immersion  objective.  The 
number  of  cells  in  the  field  of  vision  are  counted.  The 
leucocytes  in  10  fields  in  different  parts  of  the  prepara- 
tion are  counted  and  the  average  per  field  determined. 
The  limit  for  normal  milk  is  10  leucocytes  to  the  field. 

Stewart's  Test. — Special  tubes,  closed  with  a  rubber 
stopper  at  the  bottom,  are  used  for  this  test,  and  a  spe- 
cial centrifuge  head  is  also  required.  One  c.c.  of  milk  is 
placed  in  the  tube  and  centrifugalized  for  ten  minutes. 
This  throws  the  sediment  down  on  the  upper  surface  of 
the  rubber  stopper  at  the  bottom  of  the  tube.  The  stop- 


282        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

per  is  removed,  and  the  sediment  spread  on  a  glass  slide 
by  rubbing  the  stopper  over  an  area  of  1  square  centi- 
metre. The  preparation  is  dried  in  the  air,  stained  2 
minutes  with  Jenner's  blood  stain  and  examined  under 
the  microscope  with  the  1/12  oil-immersion  objective  and 
a  No.  3  ocular.  The  leucocytes  in  10  fields  are  counted. 
An  average  of  23  cells  to  the  field  is  the  limit  for  normal 
milk.  If  the  average  number  of  cells  to  the  field  is  mul- 
tiplied by  4400  the  approximate  number  of  cells  per  c.c. 
is  obtained. 

Doane-Buckley  Method. — 10  c.c.  of  milk  is  centrifu- 
galized  for  10  minutes  in  a  graduated  sediment  tube,  after 
which  the  cream  and  separated  milk  is  drawn  off  with  a 
pipette  down  to  the  1  c.c.  mark.  A  drop  of  saturated  al- 
coholic solution  of  methylene  blue  is  mixed  with  the  re- 
maining portion  and  the  mixture  is  allowed  to  stand  one 
minute  to  stain  the  cells.  One  drop  of  this  mixture  is 
placed  in  a  Thoma-Zeiss  blood-counting  apparatus  and 
the  number  of  leucocytes  per  c.c.  determined.  The  limit 
for  normal  milk  is  500,000  per  c.c. 

Trommsdorff  Test. — For  this  test  a  special  sediment 
tube  is  used  which  is  drawn  out  at  the  lower  end  into  a 
small  capillary  tube  with  twenty  graduations,  each  grad- 
uation representing  0.01  per  cent.  10  c.c.  of  milk  is 
placed  in  the  tube  and  centrifugalized  for  10  minutes. 
The  volume  and  color  of  the  sediment  in  the  capillary 
tube  are  then  noted.  The  limit  for  sediment  in  milk  from 
individual  cows  in  normal  condition  is  0.1  per  cent,  and 
the  color  should  be  white  or  grayish  white.  If  the  sedi- 
ment exceeds  this  amount  and  is  of  a  yellowish-color,  the 
presence  of  mastitis  secretion  is  indicated  and  the  sedi- 
ment should  then  be  examined  microscopically  to  deter- 
mine whether  it  consists  largely  of  leucocytes  or  of  debris 


METHODS  OF  EXAMINING  MILK 


283 


and  if  streptococci  are  present.  In  fresh  cows,  the  sedi- 
ment is  usually  of  a  grayish-white  or  white  color  and  or- 
dinarily does  not  exceed  0.08  per  cent;  sometimes  the 
sediment  is  red,  which  is  an  indication  of  the  presence  of 
red  blood  cells. 

In  all  of  these  tests  the  kind  of  leucocytes  should  re- 
ceive attention  as  well  as  the  number. 
A  preponderance  of  polymorphonu- 
clear  leucocytes  is  very  significant, 
since  in  mastitis  three-fourths  and 
more  of  the  cells  are  of  this  type.  The 
clumping  or  grouping  of  the  cells  is 
also  characteristic  of  milk  containing 
mastitis  secretion.  There  is  an  in- 
creased number  of  epithelial  cells  in 
the  milk  of  cows  affected  with  mas- 
titis; in  catarrh  of  the  milk  cistern, 
nests  of  elongated  epithelial  cells  may 
be  observed  in  the  sediment. 

When  an  excessive  number  of  leu- 
cocytes is  found  in  market  milk,  with 
a  preponderance  of  polymorphonu- 
clear  cells  showing  the  characteristic 
clumping  or  grouping,  an  examination 
of  the  herd  from  which  the  milk  came 


FIG.  39.-sediment  tube 


.,,  -IT  T       i  .1  />    *n  the  capillary  extension 

will  usually  disclose  the  presence  of  »*  the  bottom. 
mastitis  or  other  suppurative  condition.  In  such  cases, 
however,  it  must  be  remembered  that  leucocytes  are  in- 
creased in  number  in  the  milk  at  the  beginning  and  near 
the  end  of  lactation  and  following  incomplete  or  delayed 
milking.  Heating  milk  to  60°  C.  (140°  F.)  or  above 
also  increases  the  number  of  leucocytes  in  the  sediment. 
When  the  number  of  leucocytes  in  market  milk  falls 


284        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

within  the  limits  set  for  normal  milk,  the  possible  pres- 
ence of  mastitis  secretion  is  not  excluded. 

The  presence  of  numerous  streptococci  in  connection 
with  an  excess  of  leucocytes  is  strong  evidence  that  the 
milk  contains  secretion  from  an  inflamed  udder.  Milk 
may  contain  non-pathogenic  (Streptococcus  lacticus)  as 
well  as  pathogenic  streptococci  but,  as  was  first  pointed 
out  by  Bergy,  the  streptococci  may  be  regarded  as  path- 
ogenic when  they  are  associated  with  a  large  number  of 
polymorphonuclear  leucocytes,  especially  if  they  are  in 
long  chains.  The  presence  of  cocci,  diplococci,  or  short 
chains  within  the  cells  is  also  significant.  Furthermore, 
the  pathogenic  streptococci  usually  form  longer  chains 
than  the  non-pathogenic,  chains  of  Streptococcus  lacticus 
rarely  containing  more  than  6  or  8  organisms.  (See 
Figs.  5  and  6) .  According  to  Ernst,  the  mastitis  strep- 
tococci can  be  recognized  by  the  shape  of  the  individual 
cocci  and  the  length  of  the  chain.  ( See  page  53. ) 

The  leucocyte  tests  are  more  reliable  for  individual 
milk  than  for  market  milk.  In  comparisons  of  the  leuco- 
cyte tests  with  the  catalase  test  in  the  examination  of  in- 
dividual milk  to  discover  evidence  of  mastitis,  the  catalase 
test  has  proven  the  more  accurate. 

BOILING  TEST 

A  small  quantity  of  milk  is  placed  in  a  vessel  and 
boiled,  after  which  it  is  examined  for  flakes  or  curds.  In 
the  laboratory,  about  10  to  15  c.c.  of  milk  is  placed  in  a 
test  tube,  which  is  then  held  over  a  Bunsen  flame  until  the 
milk  boils.  Fresh,  normal  market  milk  will  not  curdle. 
When  curdling  occurs,  it  indicates  that  the  milk  has  un- 
dergone excessive  acid  fermentation,  either  because  it  is 
stale,  or  was  produced  under  unclean  conditions,  or  was 


METHODS  OF  EXAMINING  MILK  285 

not  properly  cooled  and  cared  for.  When  tested  in  this 
manner,  milk  will  curdle  before  a  sour  taste  is  apparent 
and  several  hours  before  it  will  curdle  spontaneously.  If 
boric  acid  has  been  added  to  the  milk  as  a  preservative 
this  will  increase  the  acidity  and  influence  the  test.  Sali- 
cylic acid  generally  has  no  influence  because  it  is  not  usu- 
ally added  in  sufficient  quantity. 

Milk  also  curdles  when  boiled  when  there  is  an  excess 
of  albumin  or  globulin  present.  In  normal  milk,  albumin 
and  globulin  are  not  present  in  sufficient  amount  to  make 
curdling  visible  when  the  milk  is  boiled.  The  udder  se- 
cretion from  individual  cows  will  curdle  on  boiling  for 
two  to  four  days  after  parturition.  Boiling  will  also  cur- 
dle milk  from  cows  affected  with  inflammation  of  the 
udder,  cowpox,  and  nymphomania.  During  oestrum  the 
milk  sometimes  curdles  when  boiled.  It  is  necessary  to 
test  the  milk  of  the  individual  cow  to  obtain  a  positive 
reaction  in  these  cases.  If  the  milk  from  the  affected  cow 
is  mixed  with  the  milk  from  other  cows  in  the  herd,  the 
albumin  or  globulin  may  be  so  diluted  that  curdling  will 
not  be  apparent. 

ALCOHOL  TEST 

In  applying  the  alcohol  test,  exactly  equal  quantities 
by  volume  of  milk  and  68  per  cent,  alcohol  are  mixed  to- 
gether, after  which  the  mixture  is  examined  for  flakes  or 
curds.  The  flakes  may  be  quite  small  and  must  be  looked 
for  carefully.  The  test  is  most  conveniently  made  with 
a  test  tube  marked  for  5  c.c.  and  10  c.c.  The  tube  is  filled 
to  the  5  c.c.  mark  with  68  per  cent,  alcohol,  and  to  the  10 
c.c.  mark  with  milk,  and  the  two  fluids  are  then  mixed 
by  shaking.  Milk  should  not  be  tested  when  cold,  be- 
cause at  low  temperatures  casein  has  a  tendency  to  clump 
and  form  flakes.  The  flakes  of  fat  formed  when  milk  is 


286        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

agitated  must  not  be  mistaken  for  curds  or  flakes  result- 
ing from  the  alcohol  reaction. 

The  68  per  cent,  alcohol  is  made  by  mixing  68  parts  of 
absolute  alcohol  with  32  parts  of  distilled  water.  The 
alcohol  should  be  neutral.  This  can  be  determined  by 
adding  a  few  drops  of  phenolphthalein  solution  to  a  small 
quantity  of  the  alcohol  and  then  running  in  a  drop  of 
tenth-normal  sodium  hydroxide  solution.  If  the  alcohol 
is  neutral  the  mixture  will  assume  a  permanent  pink 
color. 

Fresh  normal  market  milk  will  not  curdle  when 
tested  in  this  manner.  Milk  which  has  undergone  acid 
fermentation,  or  which  has  been  acted  upon  by  the  rennet- 
like  ferment  produced  by  certain  species  of  bacteria,  or 
which  has  undergone  a  combined  acid  and  rennet  fermen- 
tation, will  curdle  when  these  processes  have  operated  to 
a  certain  extent.  A  positive  reaction  therefore  results 
when  the  milk  has  undergone  a  certain  degree  of  bacterial 
decomposition  and  is  an  indication  that  the  milk  is  old,  or 
that  it  was  produced  under  unclean  conditions,  or  that  it 
was  not  properly  cooled  and  cared  for. 

The  milk  of  individual  cows  will  give  a  positive  reac- 
tion for  from  four  to  twelve  days  after  parturition  and 
near  the  end  of  lactation.  For  a  rather  long  time  after 
abortion,  the  milk  will  also  give  a  positive  reaction.  Milk 
from  cows  with  diseased  udders  will  react  positively  be- 
fore any  clinical  symptoms  are  apparent  and  also  for  a 
time  after  the  disease  has  clinically  healed.  Milk  from 
cows  affected  with  diseases  or  injuries  of  the  genital  tract, 
diseases  of  the  digestive  tract,  or  advanced  tuberculosis 
will  also  usually  give  a  positive  reaction  to  the  alcohol 
test,  but  not  always.  It  appears  that  a  positive  reaction 
occurs  in  these  cases  only  when  pathological  products  are 


METHODS  OF  EXAMINING  MILK  287 

absorbed  from  the  diseased  area  and  eliminated,  in  part 
at  least,  through  the  udder.  While  a  negative  reaction 
may  not  always  indicate  the  entire  absence  of  disease,  the 
presence  of  any  diseased  condition  which  affects  the 
udder  directly  or  indirectly  is  indicated  by  a  positive  re- 
action, excluding,  of  course,  cows  which  are  "fresh,"  near 
the  end  of  lactation,  in  heat,  or  which  have  recently 
aborted. 

The  alcohol  test  is  a  more  delicate  test  for  bacterial 
decomposition  and  for  the  presence  of  inflammatory  and 
other  pathological  products  than  the  boiling  test  and  will 
give  a  positive  reaction  when  the  boiling  test  is  negative. 

CATALASE  TEST 

The  amount  of  catalase  in  milk  is  measured  by  the 
amount  of  oxygen  which  is  separated  when  a  measured 
quantity  of  hydrogen  peroxide  is  added  to  a  certain  quan- 
tity of  milk.  Different  forms  of  apparatus  are  used  for 
collecting  and  measuring  the  oxygen,  the  one  most  com- 
monly used  being  the  Gerber-Lobeck  apparatus. 

The  quantity  of  oxygen  separated  will  depend  not 
only  on  the  amount  of  catalase  in  the  milk,  but  also  upon 
the  amount  of  hydrogen  peroxide  added.  The  quantity 
of  oxygen  separated  increases  with  the  amount  of  hydro- 
gen peroxide  added  up  to  a  certain  point,  but  if  hy- 
drogen peroxide  is  present  in  excess  of  this  amount  it 
will  exert  a  depressing  effect  upon  the  ferment.  For 
this  reason  it  is  necessary  to  standardize  the  hydrogen 
peroxide  solution  used,  and  since  the  solution  is  unstable 
it  must  be  standardized  from  time  to  time. 

A  1  per  cent,  solution  of  hydrogen  peroxide  is  used 
in  the  test.  The  ordinary  preparations  of  hydrogen  per- 
oxide are  3  per  cent,  solutions  and  must  therefore  be 


288        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 


diluted  with  twice  the  quantity  of 
water  to  prepare  a  1  per  cent,  solu- 
tion. Distilled  water  or  well-boiled 
and  filtered  water  should  be  used. 
For  example:  100  c.c.  hydrogen  per- 
oxide, 200  c.c.  distilled  water.  The 
solution  should  be  standardized  by 
titration  with  a  tenth-normal  potas- 
sium permanganate  solution,  as 
follows: 

Ten  c.c.  of  the  hydrogen  peroxide 
solution  is  mixed  with  90  c.c.  of  dis- 
tilled or  boiled  water.  Of  this  solu- 
tion, 10  c.c.  is  placed  in  a  beaker 
with  10  c.c.  of  dilute  sulphuric  acid. 
The  dilute  sulphuric  acid  is  prepared 
by  adding  400  c.c.  of  distilled  water 
to  100  c.c.  of  sulphuric  acid  with  a 
specific  gravity  of  1.82  to  1.825. 
About  5  c.c.  of  the  tenth-normal  solu- 
tion of  potassium  permanganate  is  run 
4o.— Gerber-Lobeck  ^to  the  beaker  f rom  a  burette  and  it 


through  w 

capes  from  the  middle  to  the 


lafi6  is  then  added  slowly  until  the  solution 

2.  Volumeter, showing  (a)  the          _  . 

middle  tube,  with  scale;  (6)  takes  on  a  pale  violet  color  which 

the  inner  tube,  through  which 

the  oxygen  ascends  from  the  rpmoino  offpr*  ctirrmcr  Ahrmf  (\   o  r* 

bottle  to  the  top  of  the  middle  reiUdrllla  d,L  LCI  blllilllg.  ^LUUUl  D    C.L. 

tube,  and  (c)  the  openings         .-i-i  -i                    •  j    /»              -  ,           •* 

rhich  the  water  es-  will  be  required  for  Si  1  per  cent,  solu- 
tion of  hydrogen  peroxide.  Each 
c.c.  of  the  tenth-normal  potassium 
permanganate  solution  is  equal  to 
0.0017008  gram  hydrogen  peroxide. 
Example:  0.0017008  X  6 P=> 0.0102048  X  10Q  =  1.02 
per  cent,  hydrogen  peroxide. 

The  hydrogen  peroxide  solution  should  be  kept  in  an 


c.c.  mark  and  elevated  it  a 
corresponding  degree  in  the 
outer  tube.  (Courtesy  Cor- 
nell Veterinarian.) 


METHODS  OF  EXAMINING  MILK  289 

amber  colored  bottle,  well  stoppered  and  in  a  cool  place. 
High  temperatures  break  up  the  compound.  The  bottle 
should  be  closed  immediately  after  being  opened  to  draw 
off  any  of  the  solution.  The  solution  must  be  tested  by 
titration  from  time  to  time  in  order  to  insure  accurate  re- 
sults. 

To  overcome  the  inconvenience  of  frequent  tests  of 
the  hydrogen  peroxide  solution,  the  N.  Gerber  Co.,  of 
Leipsig,  Germany,  has  prepared  a  tablet  containing  the 
hydrogen  peroxide  in  more  stable  form.  One  of  these 
tablets  dissolved  in  5  c.c.  of  water  makes  a  1  per  cent, 
solution  of  hydrogen  peroxide.  (It  has  also  been  estab- 
lished by  extensive  experiments  that  one  of  these  tablets 
added  to  10  c.c.  of  milk  will  give  the  same  result  as  3  c.c. 
of  a  1  per  cent,  hydrogen  peroxide  solution  in  9  c.c.  of 
milk). 

The  test  is  made  as  follows:  1.  The  bottles  must 
be  well  cleaned  and  sterilized  by  boiling  for  15  minutes 
before  using.  The  use  of  water  containing  calcium  must 
be  avoided.  If  not  used  at  once  the  bottles  are  to  be 
tightly  corked  with  rubber  stoppers,  which  are  also  to 
be  sterilized  by  boiling.  The  bottles  may  be  closed  with 
cotton  plugs  and  sterilized  in  a  hot-air  sterilizer.  Pipettes 
should  be  sterilized  before  beginning  a  series  of  tests. 
The  pipette  used  for  measuring  the  milk  should  be 
washed  out  with  cold  water  and  then  sterilized  by  filling 
it  with  boiling  water  after  each  sample  of  milk  is  meas- 
ured. 

2.  Three  c.c.  of  a  1  per  cent,  solution  of  hydrogen 
peroxide  is  placed  in  the  bottle ;  then  9  c.c.  of  the  milk  to 
be  tested  is  added.  The  bottle  is  numbered  to  correspond 
with  the  sample  of  milk.  In  testing  individual  milk,  it 
is  recommended  that  the  sample  be  taken  from  the  entire 

19 


290        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

quantity  of  milk  obtained  at  a  milking,  or  from  the  total 
quantity  obtained  from  each  quarter,  if  it  is  desired  to  test 
each  quarter  separately;  but  when  this  is  not  convenient, 
50  to  100  c.c.  of  milk  may  be  drawn  from  each  quarter 
directly  into  a  sterile  sample  bottle,  after  discarding  the 
first  three  expressions  from  each  teat.  In  either  case,  the 
sample  should  be  thoroughly  mixed  before  the  amount 
required  for  the  test  is  drawn  off. 

3.  The  volumeter,  properly  filled  with  water  free 
from  air  bubbles,  is  closed  at  the  top  with  a  rubber  stop- 
per and  is  then  inserted  into  the  perforated  stopper  of  the 
bottle.     The  perforated  stopper  must  be  forced  down 
sufficiently  to  close  the  small  hole  in  the  neck  of  the  bot- 
tle.   The  fluids  are  mixed  by  gently  whirling  the  bottle, 
care  being  taken  not  to  wet  the  stopper. 

4.  The  apparatus  is  set  aside  at  a  temperature  of  20 
to  25°  C.;  in  winter  a  water  bath  is  necessary,  but  only 
the  bottle  should  be  placed  in  the  water.     The  rubber 
stopper  in  the  upper  end  of  the  volumeter  should  be  re- 
moved in  order  to  avoid  any  counter-pressure  against 
the  water  being  forced  from  the  middle  chamber  of  the 
volumeter  to  the  outer  by  the  pressure  of  the  oxygen 
separated  from  the  hydrogen  peroxide  in  the  bottle.    The 
bottle  is  then  permitted  to  stand  for  two  hours,  when  the 
amount  of  oxygen  is  read  off. 

5.  The  amount  of  oxygen  separated  is  indicated  by 
the  extent  to  which  the  water  in  the  inner  tube  of  the 
volumeter  has  been  forced  downward.     Before  taking 
the  reading  as  final,  the  bottle  should  be  gently  whirled 
until  the  volume  of  oxygen  remains  constant.    Without 
such  agitation,  some  of  the  gas  may  remain  in  the  bottle, 
adherent  to  the  fluid,  and  the  reading  will  not  give  the 


METHODS  OF  EXAMINING  MILK  291 

correct  result.  Increases  of  0.3  to  1  c.c.  have  been  ob- 
served after  agitation. 

6.  After  the  reading  is  taken,  the  volumeter  is  dis- 
connected from  the  bottle,  the  stopper  inserted  in  the  top, 
and  the  water  forced  from  the  outer  to  the  middle  tube 
by  pressure  on  the  stopper  until  the  two  columns  of  water 
are  level  with  each  other.  The  volumeter  is  then  ready  to 
be  used  again.  The  bottle  is  emptied  and  cleaned  and 
sterilized  for  the  next  test. 

Milk  from  one  or  several  cows  in  normal  condition, 
tested  within  three  hours  after  being  drawn  from  the 
udder,  will  not  show  over  3  c.c.  of  oxygen  at  the  end  of 
the  second  hour.  If  the  milk  is  not  tested  within  three 
hours,  the  oxygen  reading  will  be  in  excess  of  this  figure, 
because  the  catalase  in  the  milk  at  the  time  it  was  secreted 
will  have  been  added  to  by  that  produced  by  the  bacteria 
in  the  milk.  According  to  Faitelowitz  and  others,  if  2  per 
cent,  of  chloroform  is  added  to  the  milk  the  power  or  ac- 
tivity of  the  catalase  existing  at  the  time  is  not  affected, 
while  the  secretion  of  catalase  by  bacteria  is  prevented. 

Certain  physiological  conditions  cause  an  increase  in 
the  catalase.  Colostrum,  milk  for  4  to  5  days  up  to  3 
weeks  after  calving,  and  milk  from  "strippers"  yielding 
only  a  quart  or  less  a  day  give  a  higher  oxygen  reading 
than  is  normal  for  milk  at  other  stages  of  lactation.  The 
oxygen  reading  is  also  increased  after  sudden  or  pro- 
nounced changes  in  feed,  following  incomplete  milking 
and  stasis  of  milk,  and  sometimes  in  oestrum  when  the 
cow  is  nervous  and  excitable. 

In  disease  of  the  udder,  when  individual  milk  is  tested, 
the  oxygen  reading  is  above  normal  before  any  clinical 
symptoms  are  apparent  and  before  there  are  any  visible 
changes  in  the  appearance  of  the  milk.  The  reading 


292        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

continues  high  for  a  time  after  the  clinical  symptoms 
have  disappeared.  The  increase  of  catalase  in  mastitis 
is  not  always  due  to  the  bacteria  present.  Koning  has 
demonstrated  that  the  streptococci  of  mastitis  do  not  pro- 
duce catalase,  but  that  the  toxins  they  excrete  irritate 
the  gland  tissue  and  cause  an  increased  transudation  of 
blood  serum  and  emigration  of  leucocytes,  thus  increas- 
ing the  catalase  in  the  milk.  The  catalase  may  also  be 
increased  in  purely  traumatic  or  non-bacterial  mastitis. 
When  only  one  quarter  of  an  udder  is  visibly  diseased, 
the  milk  from  the  other  quarters  which  are  apparently 
healthy  may  show  a  high  catalase  reaction.  The  catalase 
test  cannot  be  relied  upon  to  discover  mastitis  when  mixed 
milk  is  examined.  Mixed  milk  containing  5  per  cent, 
of  milk  from  a  diseased  udder  will  show  a  high  oxygen 
reading,  but  if  the  dilution  is  greater  than  this  there  will 
be  nothing  abnormal  in  the  reaction  (Gerber) . 

In  general  disease,  and  when  disease  is  present  in 
other  organs  than  the  udder,  the  oxygen  reading  of  in- 
dividual milk  is  usually,  but  not  always,  high.  In  these 
conditions,  according  to  Mogendorff,  the  catalase  in  the 
milk  is  increased  when  the  udder  assists  in  the  elimina- 
tion of  the  products  of  disease,  the  toxins  or  other  disease- 
products  irritating  the  gland  tissue  and  causing  an  un- 
usual amount  of  blood  serum  and  leucocytes  to  pass  over 
into  the  milk.  The  presence  of  pathological  processes  in 
the.body  is  often  indicated  by  an  increase  in  the  catalase 
in  the  milk  before  they  are  manifested  by  clinical  symp- 
toms, while  in  diseases  in  which  resolution  is  not  complete 
the  catalase  may  be  increased  in  the  milk  after  all  clinical 
symptoms  have  disappeared.  As  a  rule,  there  is  an  in- 
crease of  catalase  in  the  milk  in  all  diseases  accompanied 
by  a  high  fever;  when  non-encapsulated  purulent  areas 


METHODS  OF  EXAMINING  MILK  293 

are  present  in  the  body,  as  in  traumatic  pericarditis,  ab- 
scesses, f  urunculosis,  panaritium ;  in  diseases  of  the  diges- 
tive apparatus  such  as  gastro-intestinal  catarrh,  constipa- 
tion, tympanites,  enteritis,  etc. ;  when  the  organs  of  elim- 
ination are  affected,  as  in  icterus,  interference  with  the 
excretion  of  urine,  constipation ;  in  acute  and  chronic  in- 
flammation of  the  uterus ;  in  peritonitis,  and  in  advanced 
tuberculosis,  even  when  the  udder  is  free  from  the  disease. 
The  catalase  will  also  be  increased  in  the  milk  of  all  cows 
reacting  to  tuberculin  for  several  days  after  the  injection. 

Whether  a  high  catalase  reaction  is  due  to  disease  in 
the  udder  or  to  disease  in  another  part  of  the  body  may 
be  determined  by  centrifugalizing  the  milk  and  examin- 
ing the  sediment.  If  the  disease  is  in  the  udder,  leuco- 
cytes will  be  present  in  excess  of  the  usual  number. 
Gratz  and  Naray  observed  that  when  the  oxygen  reading 
is  high  in  the  milk  of  cows  which  have  recently  "fresh- 
ened," the  sediment,  as  obtained  by  the  Trommsdorff 
method,  may  be  low  in  volume  but  of  a  red  color,  the  high 
catalase  reaction  being  due  to  the  presence  of  red  blood 
cells.  For  a  time  following  parturition,  red  blood  cells 
may  enter  the  milk  by  diapedesis  or  by  rupture  of  blood 
vessels.  They  therefore  regard  it  as  necessary  to  examine 
the  sediment  before  deciding  as  to  the  cause  of  a  high 
catalase  reaction. 

Fresh  market  milk  from  cows  in  normal  condition, 
which  has  been  properly  cooled  and  cared  for,  should 
never  show  over  4  c.c.  of  oxygen  at  the  end  of  the  second 
hour  (Gerber).  When  market  milk  shows  a  higher 
oxygen  reading,  the  indication  is  that  the  original  bacter- 
ial contamination  has  been  excessive,  or  that  the  milk  is 
old,  or  that  it  may  have  pathological  milk  or  colostrum 
mixed  with  it.  A  large  amount  of  gas  (CO2)  will  be 


294        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

separated  if  sodium  bicarbonate  has  been  used  as  a  pre- 
servative. The  catalase  test  is  not  as  suitable  for  the  ex- 
amination of  market  milk  as  some  of  the  other  methods, 
but  it  is  one  of  the  most  delicate  tests  for  detecting  path- 
ological conditions  when  individual  milk  is  examined. 
REDUCTASE  TEST 

In  this  test,  methylene  blue  solution  and  milk  are 
mixed  together  and  the  amount  of  reductase  present,  or 
the  reduction  power,  is  indicated  by  the  length  of  time 
required  for  the  blue  color  to  disappear.  Different  prep- 
arations of  methylene  blue  vary  in  composition  and  it  is 
therefore  recommended  that  Merck's  B  extra  methylene 
blue  be  always  used.  The  solution  is  prepared  as  fol- 
lows :  methylene  blue  is  added  to  absolute  alcohol  to  sat- 
uration; 5  c.c.  of  this  saturated  alcoholic  solution  is  then 
added  to  195  c.c.  of  sterile  distilled  water;  this  is  the  so- 
lution used  in  making  the  test.  The  saturated  alcoholic 
solution  is  rather  unstable,  and  Barthel  and  O.  Jensen 
therefore  recommend  that  the  test  solution  be  made  with 
tablets  of  Merck's  B  extra  methylene  blue  prepared  by 
Blauenf eld  and  Tvede,  of  Copenhagen,  Denmark.  One 
tablet  is  dissolved  in  200  c.c.  of  sterile  distilled  water. 
The  solution  will  keep  two  weeks.  When  milk  is  tested 
with  the  tablet  solution,  the  reduction  time  will  be  shorter 
than  when  it  is  tested  with  the  solution  made  from  the 
saturated  alcoholic  solution,  because  the  tablet  solution 
contains  less  methylene  blue. 

Ordinary  test  tubes  are  used  in  making  the  test. 
These  should  be  cleaned,  plugged  with  cotton  and  steril- 
ized. The  pipettes  used  in  measuring  the  milk  and  the 
methlyene  blue  solution  should  also  be  cleaned  and  steril- 
ized. After  each  sample  of  milk  is  measured,  the  pipette 
used  for  this  purpose  should  be  rinsed  with  cold  water 


METHODS  OF  EXAMINING  MILK  295 

and  sterilized  by  drawing  boiling  water  into  it  several 
times. 

The  test  is  made  as  follows :  The  milk  to  be  tested  is 
heated  to  a  temperature  of  45  to  48°  C.  (113  to  118°  F.) ; 
%  c.c.  of  the  methylene  blue  solution  is  placed  in  the 
test  tube  and  20  c.c.  of  the  milk  is  added.  The  test  tube  is 
closed  with  the  cotton  plug,  placed  in  a  water  bath  or 
incubator  at  38  to  39°  C.  (100.4  to  102°  F.),  and  ob- 
served at  frequent  intervals  to  note  the  time  of  decolori- 
zation.  If  the  methylene  blue  solution  is  placed  in  the 
tube  first  and  the  milk  afterward,  the  two  fluids  will  be 
thoroughly  mixed  and  there  will  be  no  opportunity  for 
a  part  of  the  methylene  blue  solution  to  be  absorbed  by 
the  cotton  plug.  It  is  not  necessary  to  cover  the  mixture 
with  a  layer  of  paraffine  oil,  as  was  formerly  recom- 
mended, because  the  difference  in  reduction  time  caused 
by  the  exclusion  of  oxygen  is  not  sufficient  to  be  taken 
into  consideration  in  routine  milk  testing. 

Several  investigators  have  compared  the  reduction 
time  of  market  milk  with  the  number  of  bacteria  as  de- 
termined by  the  plate  method.  O.  Jensen,  using  a  test 
solution  prepared  from  a  saturated  alcoholic  solution  of 
methylene  blue,  found  the  relations  to  be  as  follows : 

1.  Decolorization  in  7  hours  or  over,  100,000  bacteria 
per  c.c. 

2.  Decolorization  in  from  2  to  7  hours,  100,000  to 
300,000  bacteria  per  c.c. 

3.  Decolorization  in  from  %  to  2  hours,  300,000  to 
20,000,000  bacteria  per  c.c. 

4.  Decolorization  in  less  than  %  hour,  49,000,000  to 
264,000,000  bacteria  per  c.c. 

In  testing  market  milk  with  methylene  blue  solution 
prepared  from  tablets,  O.  Jensen  and  Barthel  found  the 


296        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

reduction  time  and  the  number  of  bacteria  per  c.c.  to  com- 
pare as  follows : 

1.  Decolorization  in  5%  hours  or  over,  less  than 
500,000  bacteria  per  c.c. 

2.  Decolorization  in  from  2  to  5%  hours,  500,000 
to  4,000,000  bacteria  per  c.c. 

3.  Decolorization  in  from  20  minutes  to  2  hours, 
4,000,000  to  20,000,000  bacteria  per  c.c. 

4.  Decolorization  in  20  minutes  or  less,  over  20,000,- 
000  bacteria  per  c.c. 

These  figures  do  not  apply  to  milk  that  has  been 
heated. 

The  reduction  time  of  market  milk  agrees  in  a  general 
way  with  the  number  of  bacteria  contained  in  the  milk 
and  is  a  very  good  index  to  the  "keeping  qualities"  or 
stability  of  milk.  The  reductase  test  is  not  to  be  de- 
pended upon  to  detect  pathological  milk.  While  mastitis 
milk  usually  decolorizes  in  a  shorter  time  than  normal 
milk,  this  does  not  occur  in  all  cases. 

O.  Jensen  has  combined  the  reductase  test  with  the 
fermentation  test. 

FERMENTATION-REDUCTASE  TEST 

This  is  a  combination  of  the  fermentation  and  re- 
ductase tests  which  was  first  proposed  by  O.  Jensen. 
One-half  c.c.  of  methylene  blue  solution  is  placed  in  a  test 
tube  with  20  c.c.  of  milk,  the  tube  is  placed  in  an  incubator 
and  kept  under  observation  until  decolorization  occurs, 
as  in  the  reductase  test.  In  addition,  the  test  tube  is 
kept  in  the  incubator  until  curdling  occurs,  and  the  type 
of  curd  is  then  noted.  Methylene  blue  in  large  quantity 
inhibits  the  development  of  bacteria,  especially  the  lactic 
acid  bacteria,  but  in  the  quantity  used  in  this  test  the 
effect  is  practically  negligible. 


METHODS  OF  EXAMINING  MILK  297 

A  quickly  reducing  milk  very  frequently  produces  a 
good  curd  (jelly-like)  because  in  milk  rich  in  bacteria 
the  lactic  acid  bacteria  are  often  so  numerous  that  they 
inhibit  the  growth  of  the  other  species.  But  a  milk  may 
reduce  quickly  and  at  the  same  time  produce  a  bad  curd 
(gaseous  or  peptonized)  ;  such  milk  is  extremely  objec- 
tionable. On  the  other  hand,  a  slowly  reducing  milk  may 
produce  a  peptonized  curd.  This  is  because  milk  pro- 
duced under  cleanly  conditions  is  exposed  to  a  compara- 
tively slight  bacterial  contamination  and  the  udder  cocci 
consequently  predominate.  When  such  milk  is  kept  at 
a  low  temperature  the  peptonizing  bacteria  (udder  cocci) 
will  develop  more  rapidly  than  the  others  and  it  will  con- 
tain few  lactic  acid  bacteria.  For  these  reasons,  it  has 
been  recommended  by  Barthel  and  O.  Jensen  that  milk 
with  a  reduction  time  of  5%  hours  or  over  should  not 
be  condemned  as  bad  on  account  of  a  peptonized  curd. 

DIASTASE  TEST 

Koning  devised  a  method  for  the  quantitative  deter- 
mination of  diastase.  The  reagents  used  are  a  solution  of 
starch  and  a  solution  of  iodine.  The  starch  solution  is 
prepared  by  adding  1  gramme  of  soluble  starch  to  100  c.c. 
of  sterile  distilled  water,  warming,  and  shaking  the  mix- 
ture to  bring  about  solution.  The  iodine  solution  is  pre- 
pared by  dissolving  1  gramme  of  iodine  and  2  grammes 
of  potassium  iodide  in  300  c.c.  of  distilled  water.  The  test 
is  made  as  follows : 

Ten  c.c.  of  milk  is  placed  in  each  of  five  test  tubes. 
0.05  c.c.  of  the  starch  solution  is  added  to  the  first  tube,  0.1 
c.c.  to  the  second,  0.2  c.c.  to  the  third,  0.25  c.c.  to  the 
fourth  and  0.3  c.c.  to  the  fifth.  The  tubes  are  placed  in 
a  water  bath  at  45°  C.  for  30  minutes,  after  which  1  c.c. 
of  the  iodine  solution  is  added  to  each  tube.  If  all  of  the 


298        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

starch  has  been  digested  the  mixture  in  the  tube  assumes 
a  citron-yellow  color ;  if  any  starch  remains  a  blue  color 
will  appear.  According  to  Koning,  normal  milk  will 
digest  the  starch  in  the  first  two  or  the  first  three  tubes; 
a  higher  diastatic  power  indicates  mastitis,  while  a  lower 
indicates  old  milk.  Others  report  that  the  diastatic  power 
of  milk  from  cows  affected  with  mastitis  is  very  variable 
and  that  the  diastase  test  cannot  therefore  be  depended 
upon  to  discover  mastitis  milk.  The  diastatic  power  is 
also  increased  in  the  colostral  period  and  near  the  end  of 
lactation.  One  observer  affirms  that  the  diastase  in  milk 
is  decreased  when  the  ration  is  rich  in  carbohydrates. 

TESTS  FOR  HEATED  MILK 

Two  tests  are  used  to  determine  whether  or  not  milk 
has  been  heated  to  80°  C.  (176°  F.)  or  above.  They  are 
as  follows: 

Storclis  Test. — 5  c.c.  of  milk  or  cream  is  placed  in  a 
test  tube,  1  drop  of  0.2  per  cent,  solution  of  hydrogen 
peroxide  containing  0.1  per  cent,  of  sulphuric  acid,  and 
2  drops  of  a  2  per  cent,  solution  of  paraphenyldiamin  are 
added,  and  the  mixture  is  shaken.  If  the  mixture  as- 
sumes an  indigo  blue  or  violet  color  immediately,  it  has 
not  been  heated  at  all  or  not  higher  than  78°  C.  (172.5° 
F. ) ;  if  it  becomes  a  light  bluish-gray  within  a  half  min- 
ute, it  has  been  heated  to  between  79  and  80°  C.  (174.2° 
to  176°  F.) ;  if  it  remains  white,  it  has  been  heated  to  at 
least  80°  C.  ( 176°  F.) .  Raw  whey  gives  a  violet  or  red- 
dish-brown color. 

Arnold's  Guaiac  Test. — A  small  quantity  of  milk  is 
placed  in  a  test  tube  and  a  little  tincture  of  guaiac  is  run 
down  the  side  of  the  tube  drop  by  drop  so  that  it  will 
not  mix  with  the  milk  but  form  a  layer  on  top  of  the  milk. 
If  the  milk  is  raw  or  has  not  been  heated  to  80°  C. 


METHODS  OF  EXAMINING  MILK  299 

(176°  F.),  a  blue  ring  is  formed  at  the  point  of  contact 
of  the  two  fluids.  If  the  milk  has  been  heated  to  80°  C. 
( 176°  F. )  or  above,  no  color  change  occurs.  The  guaiac- 
wood  tincture  is  more  reliable  than  the  guaiac-resin  tinc- 
ture of  the  U.  S.  Pharmacopoeia.  The  addition  of  a  few 
drops  of  a  weak  aqueous  solution  of  hydrogen  peroxide 
after  the  tincture  of  guaiac  has  been  run  into  the  test 
tube  increases  the  reliability  and  sharpness  of  the  test 
(Zinc),  although  if  the  guaiac  tincture  is  "ripe,"  a 
change  which  takes  place  with  age,  the  hydrogen  peroxide 
is  not  necessary.  When  the  test  is  made  with  the  tinc- 
ture alone,  the  activity  of  the  latter  should  be  tested 
against  known  raw  milk.  If  the  hydrogen  peroxide  is 
added  to  the  milk  before  the  guaiac  tincture,  or  if  too 
much  is  added,  the  reaction  will  be  retarded  or  suppressed. 
When  milk  is  strongly  acid  it  will  not  give  the  color 
reaction  at  all,  or  the  reaction  will  be  faint  or  delayed. 
Lime  water  should  be  added  to  such  milk  and  to  butter- 
milk before  testing.  Cold  milk  may  not  react  at  all 
or  very  slowly.  An  excess  of  hydrogen  peroxide  will  pre- 
vent the  reaction.  Heated  milk  to  which  formalin  has 
been  added  will  give  a  color  reaction  to  the  Storch  test 
like  raw  milk,  but  formalin  has  no  influence  on  the  guaiac 
test  when  it  is  present  in  the  quantity  used  to  preserve 
milk.  The  guaiac  test  is  also  not  affected  by  sodium 
bicarbonate,  borax,  boric  acid,  and  salicylic  acid,  but  the 
presence  of  potassium  bichromate  causes  heated  milk  to 
react  like  raw  milk  and  intensifies  the  color  reaction  of 
raw  milk. 

EXAMINATION  FOR  DIRT 

The  milk  is  filtered  through  small  cotton  discs  and 
the  larger  particles  of  dirt  present  are  collected  on  the 
surface  of  the  disc.  There  are  several  different  forms  of 


300        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

apparatus  for  making  this  test.  In  some  the  milk  is 
permitted  to  flow  through  the  filter  by  gravity,  while  in 
the  others  it  is  forced  through  by  air  pressure  from  a 
rubber  bulb.  According  to  the  quantity  of  dirt  collected 
on  the  cotton  disc  the  milk  is  classed  as  good,  medium, 
fair,  and  bad.  The  discs  are  sometimes  dried  and  mailed 
to  the  producer  for  his  examination.  There  is  no  direct 
relation  between  the  quantity  of  dirt  collected  on  the  cot- 
ton disc  and  the  bacterial  content.  Milk  which  would  be 
classed  as  good  according  to  this  test  may  have  a  high 
bacterial  content  and  vice  versa.  Furthermore,  milk  pro- 
duced under  unclean  conditions  will  test  "good  "  by  this 
test  if  it  is  well  strained  beforehand. 

Another  method  of  testing  for  dirt  is  to  place  the 
milk  in  a  conical  glass,  or  in  a  vessel  with  a  narrow  tube 
at  the  bottom,  and  measure  the  volume  of  sediment  which 
settles  to  the  bottom  after  a  certain  period;  or  the  milk 
may  be  centrifugalized  and  the  sediment  measured. 

The  visible  dirt  in  milk  consists  principally  of  par- 
ticles of  feed  and  litter,  manure,  hairs,  dandruff  and  dust. 

TEST  FOR  LACTOSE 

Glage  has  devised  a  simple  test  for  lactose  which  may 
be  applied  to  samples  of  individual  cow's  milk  or  to 
samples  of  milk  from  the  different  quarters  of  the  udder. 
It  is  made  as  follows :  Place  3  c.c.  of  milk  and  3  c.c.  of 
a  15  per  cent,  solution  of  potassium  hydroxide  in  a  test 
tube,  boil  thoroughly  and  let  stand  for  10  minutes.  When 
the  milk  contains  the  normal  amount  of  lactose  the  mix- 
ture at  first  becomes  pale  yellow  during  the  boiling, 
changing  quickly  to  dark  yellow,  to  orange,  and  then 
to  brown ;  after  standing  the  color  of  the  mixture  becomes 
coffee-brown  or  red-brown.  If  the  quantity  of  lactose  is 


QE»8ER'S         IHPR0VED  TESTER      TESTER    WITH 
SEDIMENT  WITH  COVER.  ANO 

TESTER.  STEAM  JACKET        RUBBER.   &U1.B 


PNEUMATIC 
SEDIMENT  TESTER 


FIG.  41. — Various  types  of  dirt  testers  (Wisconsin  Exp.  Station  Cir.  No.  41). 


METHODS  OF  EXAMINING  MILK  301 

below  normal  the  color  remains  yellow  or  orange.  When 
the  color  becomes  yellowish-brown  the  condition  of  the 
milk  must  be  regarded  as  doubtful.  The  presence  of  a 
large  amount  of  fat  is  likely  to  interfere  with  the  reaction 
and  it  is  therefore  best  to  remove  the  fat  from  the  milk 
before  applying  the  test.  Milk  sugar  is  decreased  in 
quantity  and  is  sometimes  entirely  absent  in  inflamma- 
tion of  the  udder.  It  is  also  reduced  in  quantity  during 
the  colostral  period  and  toward  the  end  of  lactation; 
exercise  sometimes  decreases  it.  It  is  present  in  greatest 
amount  in  the  middle  of  a  milking  and  lowest  at  the 
beginning  and  end.  Fresh  market  milk  will  always  give 
a  normal  reaction  to  this  test. 

EXAMINATION  FOR  COLORING  MATTERS 

When  the  yellow  color  of  milk  is  natural  it  is  largely 
confined  to  the  cream,  and  if  opportunity  is  given  for 
the  cream  to  rise  the  milk  beneath  it  has  a  bluish  tinge. 
But  when  the  yellow  color  is  artificial  not  only  the  cream 
but  the  milk  beneath  it  is  of  the  same  color.  Artificial 
coloring  matters  are  sometimes  added  to  milk  to  give  it 
a  rich  color  when  it  has  been  adulterated  with  water. 
Annatto,  also  called  arnatto  and  annotto;  analin  orange, 
an  azo-dye,  and  caramel  are  the  substances  most  fre- 
quently used.  Leach  recommends  the  following  pro- 
cedure for  the  detection  of  artificial  coloring: 

Place  150  c.c.  of  milk  in  a  casserole,  add  a  little  acetic 
acid  and  heat  until  curdling  occurs.  Gather  the  curd 
together  with  a  glass  rod  and  pour  off  the  whey,  or  sepa- 
rate by  filtration.  Macerate  the  curd  with  ether  in  a 
stoppered  bottle  for  several  hours.  Evaporate  the  ether 
extract  on  a  water  bath,  add  sufficient  sodium  hydroxide 
to  the  residue  to  make  it  alkaline  and  pour  the  mixture 


302        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

upon  a  small  wet  filter,  wash  the  fat  off  the  surface  with 
tap  water  and  dry  the  filter.  If  the  filter  paper  is  colored 
orange  the  presence  of  annatto  is  indicated.  The  appli- 
cation of  stannous  chloride  will  change  the  color  to  a 
characteristic  pink  if  annatto  is  present. 

If  the  curd  is  colorless  after  it  has  been  extracted 
with  ether  no  other  coloring  matter  is  present.  If  it 
is  orange  or  brownish  the  presence  of  analin  orange  or 
caramel  is  indicated.  The  curd  is  then  shaken  in  a  test 
tube  with  concentrated  hydrochloric  acid.  If  the  solu- 
tion immediately  turns  pink  the  presence  of  analin  orange 
is  indicated.  If  it  slowly  turns  blue,  this  points  to  the 
presence  of  caramel  and  the  following  test  should  be 
applied:  About  120  c.c.  of  the  milk  and  an  equal  quan- 
tity of  alcohol  are  mixed  together  and  filtered.  A  small 
quantity  of  subacetate  of  lead  is  added  to  the  filtrate  and 
the  precipitate  produced  is  collected  on  a  small  paper 
filter  which  is  dried  in  an  atmosphere  free  from  hydrogen 
sulphide.  If  caramel  is  present  the  precipitate  is  of  a 
dark  brown  color.  If  no  caramel  is  present  the  pre- 
cipitate will  be  white  or  straw  color. 


APPENDIX 

METHODS  AND   STANDARDS  FOR  THE  PRODUC- 
TION AND  DISTRIBUTION  OF 
"  CERTIFIED  MILK  "  * 

Adopted  by  the  American  Association  of  Medical  Milk  Commissions, 

May  1,  1912. 

Certified  milk  is  the  product  of  dairies  operated  in  accord- 
ance with  accepted  rules  and  regulations  formulated  by  author- 
ized medical  milk  commissions  to  insure  its  purity  and  adapta- 
bility for  infants  and  invalids. 

The  need  for  such  a  milk  was  experienced  primarily  by  those 
engaged  in  the  conservation  of  the  life  and  health  of  infants.  As 
a  result  there  was  formulated  in  1892  a  plan  whereby  certified 
milk  would  be  produced  by  a  dairyman  under  the  control  of  a 
medical  milk  commission  designated  by  a  representative  medical 
society. 

1  At  the  fifth  annual  meeting  of  the  American  Association 
of  Medical  Milk  Commissions,  held  in  Philadelphia,  May  25, 
1911,  a  committee  was  appointed  to  revise  the  manual  of  work- 
ing methods  and  standards  for  the  guidance  of  medical  milk 
commissions  in  the  supervision  of  the  production  and  distribution 
of  certified  milk.  The  committee  consisted  of  Dr.  J.  W.  Kerr 
(chairman),  Dr.  S.  McC.  Hamill,  and  Dr.  Henry  L.  Coit. 
This,  their  report,  was  adopted  at  the  sixth  annual  meeting, 
held  at  Louisville,  Kentucky,  May  1,  1912,  as  the  working 
methods  and  standards  of  the  association.  The  association 
recommends  them  to  component  commissions  as  ideal  and  to  be 
as  closely  approximated  as  possible.  The  report  includes  a 
statement  concerning  the  certified  milk  movement,  as  well  as 
the  revised  methods  and  standards,  and  is  published  for  the 
information  of  those  interested  in  the  improvement  of  public 
milk  supplies. 

Reprint  from  the  Public  Health  Reports,  vol.  xxvii,  No.  24, 
June  14,  1912. 


304        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

The  first  rules  designed  for  this  purpose  were  those  contained 
in  an  agreement  entered  into  by  a  medical  milk  commission  and 
the  dairyman  concerned.2 

The  rules  contained  in  the  original  agreement  mentioned  rep- 
resented the  essential  requirements  for  the  production  of  certified 
milk.  Following  this  precedent,  other  commissions  were  organ- 
ized, which,  in  1906,  became  federated  into  a  national  associa- 
tion known  as  the  American  Association  of  Medical  Milk  Com- 
missions. 

A  fundamental  object  of  this  Association,  was  to  bring  about 
the  uniformity  of  standards  and  their  perfection.  This  result 
has  been  reached  by  the  adoption  from  time  to  time  of  definite 
standards  relating  to  the  veterinary  inspection  of  herds  and 
farms,  the  medical  inspection  of  employees  handling  the  milk, 
and  the  bacteriological  and  chemical  examinations  as  to  quality 
and  purity.  The  requirements  with  respect  to  these  four  topics 
have  been  previously  reported  upon  by  committees  and  adopted 
by  the  Association,  and  at  its  last  annual  meeting  provision 
was  made  for  their  further  revision  and  amplification. 

ORGANIZATION  OF  MEDICAL  MILK  COMMISSIONS 

The  Medical  Milk  Commission  is  appointed  by  a  representa- 
tive medical  society,  and  acts  under  its  auspices  and  for  it,  to 
encourage  the  production  of  milk  of  the  highest  possible  stand- 
ards of  purity.  No  commission  should  be  considered  as  certi- 
fying milk  that  does  not  conform  to  the  standards  adopted  from 
time  to  time  by  the  Association  of  Medical  Milk  Commissions. 
The  commission  should  include  at  least  five  members  or  a  num- 
ber sufficient  to  become  responsible  for  and  to  carry  on  the  follow- 
ing divisions  of  work ;  (a)  The  hygiene  of  the  dairy,  as  it  relates 
to  the  production  and  distribution  of  the  milk;  (b)  the  veteri- 
nary supervision  of  the  herd;  (c)  the  medical  supervision  of  the 
employees;  (d)  the  chemical  and  bacteriological  examinations 
of  the  milk. 

2  Bui.  56,  Hygienic  Laboratory,  Public  Health  and  Marine 
Hospital  Service,  p.  615. 


APPENDIX  305 

DUTIES  OF  THE  COMMISSION 

After  its  organization  the  commission  should  designate  a 
veterinarian,  a  physician,  a  chemist,  and  a  bacteriologist  to  en- 
force its  methods  and  standards,  which  shall  be  the  prevailing 
methods  and  standards  of  the  American  Association  of  Medical 
Milk  Commissions,  and  these  officers  should  be  required  to  render 
regular  reports  of  their  inspections  and  examinations.  A  uni- 
form written  agreement  should  then  be  entered  into  with  any 
dairyman  who  is  desirous  of  undertaking  the  production  of 
certified  milk  and  the  investigation  of  whose  plant  shows  it  to 
be  properly  equipped  for  such  purpose.  Such  agreement  shall 
require  the  observance  of  the  methods  and  standards  hereinafter 
mentioned. 

Upon  receipt  of  favorable  reports  from  the  several  experts 
and  committees  which  have  made  the  investigations,  the  dairy- 
man should  be  authorized,  in  accordance  with  the  terms  of  the 
agreement,  to  employ  the  term  "  Certified  Milk,"  and  he  shall  be 
required  to  attach  to  all  containers  of  any  character  used  in  dis- 
tributing the  milk  produced  under  the  agreement  a  certificate  or 
seal  bearing  the  term  "  Certified  Milk,"  the  name  of  the  medical 
milk  commission  certifying  it,  and  the  day  or  date  of  production 
of  the  milk  contained  therein. 

HYGIENE  OF  THE  DAIRY 
Under  the  Supervision  and  Control  of  the  Veterinarian 

1.  Pastures  or  Paddocks. — Pastures  or  paddocks  to  which 
the  cows  have  access  shall  be  free  from  marshes  or  stagnant  pools, 
crossed  by  no  stream  which  might  become  dangerously  con- 
taminated, at  sufficient  distances  from  offensive  conditions  to 
suffer  no  bad  effects  from  them,  and  shall  be  free  from  plants 
which  affect  the  milk  deleteriously. 

2.  Surroundings   of  Buildings. — The   surroundings   of   all 
buildings  shall  be  kept  clean  and  free  from  accumulations  of 
dirt,  rubbish,  decayed  vegetable  or  animal  matter  or  animal 
waste,  and  the  stable  yard  shall  be  well  drained. 

3.  Location  of  Buildings. — Buildings  in  which  certified  milk 
is  produced  and  handled  shall  be  so  located  as  to  insure  proper 

20 


306         PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

shelter  and  good  drainage,  and  at  sufficient  distance  from  other 
buildings,  dusty  roads,  cultivated  and  dusty  fields,  and  all  other 
possible  sources  of  contamination;  provided,  in  the  case  of  un- 
avoidable proximity  to  dusty  roads  or  fields,  the  exposed  side 
shall  be  screened  with  cheese  cloth. 

4.  Construction    of   Stables. — The    stables    shall    be    con- 
structed so  as  to  facilitate  the  prompt  and  easy  removal  of  waste 
products.    The  floors  and  platforms  shall  be  made  of  cement  or 
other  non-absorbent  material,  and  the  gutters  .of  cement  only. 
The  floors  shall  be  properly  graded  and  drained,  and  the  manure 
gutters  shall  be  from  six  to  eight  inches  deep  and  so  placed  in 
relation  to  the  platform  that  all  manure  will  drop  into  them. 

5.  The  inside  surface  of  the  walls  and  all  interior  construc- 
tion shall  be  smooth,  with  tight  joints,  and  shall  be  capable  of 
shedding  water.     The  ceiling  shall  be  of  smooth  material  and 
dust-tight.     All  horizontal  and  slanting  surfaces  which  might 
harbor  dust  shall  be  avoided. 

6.  Drinking    and    Feed    Troughs. — Drinking    troughs    or 
basins  shall  be  drained  and  cleaned  each  day,  and  feed  troughs 
and  mixing  floors  shall  be  kept  in  a  clean  and  sanitary  condition. 

7.  Stanchions. — Stanchions  when  used  shall  be  constructed 
of  iron  pipes  or  hardwood,  and  throat  latches  shall  be  provided 
to  prevent  the  cows  from  lying  down  between  the  time  of  cleaning 
and  the  time  of  milking. 

8.  Ventilation. — The  cow  stables  shall  be  provided  with  ade- 
quate ventilation  either  by  means  of  some  approved  artificial 
device,  or  by  the  substitution  of  cheesecloth  for  glass  in  the 
windows,  each  cow  to  be  provided  with  a  minimum  of  600  cubic 
feet  of  air  space. 

9.  Windows. — A  sufficient  number  of  windows  shall  be  in- 
stalled and  so  distributed  as  to  provide  satisfactory  light  and  a 
maximum  of  sunshine;  two  feet  square  of  window  area  to  each 
600  cubic  feet  of  air  space  to  represent  the  minimum.    The  cover- 
ings of  such  windows  shall  be  kept  free  from  dust  and  dirt. 

10.  Exclusion  of  Flies,  etc. — All  necessary  measures  should 
be  taken  to  prevent  the  entrance  of  flies  and  other  insects,  and 
rats  and  other  vermin  into  all  the  buildings. 

11.  Exclusion  of  Animals  from  the  Herd. — No  horses,  hogs, 


APPENDIX  307 

dogs,  or  other  animals  or  fowls  shall  be  allowed  to  come  in  con- 
tact with  the  certified  herd,  either  in  the  stables  or  elsewhere. 

12.  Bedding. — No  dusty  or  mouldy  hay  or  straw,  bedding 
from  horse  stalls,  or  other  unclean  materials  shall  be  used  for 
bedding  the   cows.      Only   bedding  which   is   clean,   dry,   and 
absorbent  may  be  used,  preferably  shavings  or  straw. 

13.  Cleaning  Stable  and  Disposal  of  Manure. — Soiled  bed- 
ding and  manure  shall  be  removed  at  least  twice  daily,  and  the 
floors  shall  be  swept  and  kept  free  from  refuse.     Such  cleaning 
shall  be  done  at  least  one  hour  before  the  milking  time.    Manure, 
when  removed,  shall  be  drawn  to  the  field  or  temporarily  stored 
in  containers  so  screened  as  to  exclude  flies.     Manure  shall  not 
be  even  temporarily  stored  within  300  feet  of  the  barn  or 
dairy  building. 

14.  Cleaning   of  Cows. — Each  cow  in  the  herd   shall   be 
groomed  daily,  and  no  manure,  mud,  or  filth  shall  be  allowed  to 
remain  upon  her  during  milking ;  for  cleaning,  a  vacuum  appa- 
ratus is  recommended. 

15.  Clipping. — Long  hairs  shall  be  clipped  from  the  udder 
and  flanks  of  the  cow,  and  from  the  tail  above  the  brush.     The 
hair  on  the  tail  shall  be  cut  so  that  the  brush  may  be  well  above 
the  ground. 

16.  Cleaning  of  Udders. — The  udders  and  teats  of  the  cow 
shall  be  cleaned  before  milking ;  they  shall  be  washed  with  a  cloth 
and  water,  and  wiped  dry  with  another  clean  sterilized  cloth — 
a  separate  cloth  for  drying  each  cow. 

17.  Feeding. — All  foodstuffs  shall  be  kept  in  an  apartment 
separate  from  and  not  directly  communicating  with  the  cow 
barn.     They  shall  be  brought  into  the  barn  only  immediately 
before  the  feeding  hour,  which  shall  follow  the  milking. 

18.  Only  those  foods  shall  be  used  which  consist  of  fresh, 
palatable,  or  nutritious  materials,  such  as  will  not  injure  the 
health  of  the  cows  or  unfavorably  affect  the  taste  or  character 
of  the  milk.     Any  dirty  or  mouldy  food  or  food  in  a  state  of 
decomposition  or  putrefaction  shall  not  be  given. 

19.  A  well-balanced  ration  shall  be  used,  and  all  changes  of 
food  shall  be  made  slowly.     The  first  few  feedings  of  grass, 


308        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

alfalfa,  ensilage,  green  corn,  or  other  green  feeds  shall  be  given 
in  small  rations  and  increased  gradually  to  full  ration. 

20.  Exercise. — All  dairy  cows  shall  be  turned  out  for  exer- 
cise at  least  two  hours  in  each  twenty-four  in  suitable  weather. 
Exercise  yards  shall  be  kept  free  from  manure  and  other  filth. 

21.  Washing    of   Hands. — Conveniently   located    facilities 
shall  be  provided  for  the  milkers  to  wash  in  before  and  during 
milking. 

22.  The  hands  of  the  milkers  shall  be  thoroughly  washed 
with  soap,  water,  and  brush,  and  carefully  dried  on  a  clean  towel 
immediately  before  milking.    The  hands  of  the  milkers  shall  be 
rinsed  with  clean  water  and  carefully  dried  before  milking  each 
cow.     The  practice  of  moistening  the  hands  with  milk  is  for- 
bidden. 

23.  Milking  Clothes. — Clean  overalls,  jumper,  and  cap  shall 
be  worn  during  milking.    They  shall  be  washed  or  sterilized  each 
day  and  used  for  no  other  purpose,  and  when  not  in  use  they 
shall  be  kept  in  a  clean  place,  protected  from  dust  and  dirt. 

24.  Things  to  be  Avoided  by  Milkers. — While  engaged  about 
the  dairy  or  in  handling  the  milk,  employees   shall  not  use 
tobacco  nor  intoxicating  liquors.    They  shall  keep  their  fingers 
away  from  their  nose  and  mouth,  and  no  milker  shall  permit  his 
hands,  fingers,  lips,  or  tongue  to  come  in  contact  with  milk 
intended  for  sale. 

25.  During  milking  the  milkers   shall  be  careful  not  to 
touch  anything  but  the  clean  top  of  the  milking  stool,  the  milk 
pail  and  the  cow's  teats. 

26.  Milkers  are  forbidden  to  spit  upon  the  walls  or  floors 
of  stables,  or  upon  the  walls  or  floors  of  milk  houses,  or  into  the 
water  used  for  cooling  the  milk  or  washing  the  utensils. 

27.  Fore-Milk. — The  first  streams  from  each  teat  shall  be 
rejected,  as  this  fore-milk  contains  large  numbers  of  bacteria. 
Such  milk  shall  be  collected  into  a  separate  vessel  and  not  milked 
onto  the  floor  or  into  the  gutters.    The  milking  shall  be  done 
rapidly  and  quietly,  and  the  cows  shall  be  treated  kindly. 

28.  Milk  and  Calving  Period. — Milk  from  all  cows  shall  be 
excluded  for  a  period  of  forty-five  days  before  and  seven  days 
after  parturition. 


APPENDIX  309 

29.  Bloody  and  Stringy  Milk. — If  milk  from  any  cow  is 
bloody  and  stringy,  or  of  unnatural  appearance,  the  milk  from 
that  cow  shall  be  rejected  and  the  cow  isolated  from  the  herd 
until  the  cause  of  such  abnormal  appearance  has  been  determined 
and  removed,  especial  attention  being  given  in  the  meantime  to 
the  feeding  or  to  possible  injuries.    If  dirt  gets  into  the  pail,  the 
milk  shall  be  discarded  and  the  pail  washed  before  it  is  used. 

30.  Make-up  of  Herd. — No  cows  except  those  receiving  the 
same  supervision  and  care  as  the  certified  herd  shall  be  kept  in 
the  same  barn  or  brought  in  contact  with  them. 

31.  Employees  Other  Than  Milkers. — The  requirements  for 
milkers,  relative  to  garments  and  cleaning  of  hands,  shall  apply 
to  all  other  persons  handling  the  milk,  and  children  unattended 
by  adults  shall  not  be  allowed  in  the  dairy  nor  in  the  stable 
during  milking. 

32.  Straining  and  Strainers. — Promptly  after  the  milk  is 
drawn  it  shall  be  removed  from  the  stable  to  a  clean  room  and 
then  emptied  from  the  milk  pail  to  the  can,  being  strained 
through  strainers  made  of  a  double  layer  of  finely  meshed 
cheesecloth  or  absorbent  cotton  thoroughly  sterilized.     Several 
strainers  shall  be  provided  for  each  milking  in  order  that  they 
may  be  frequently  changed. 

33.  Dairy  Building. — A  dairy  building  shall  be  provided 
which  shall  be  located  at  a  distance  from  the  stable  and  dwelling 
prescribed   by   the  local   commission,    and   there   shall   be   no 
hog-pen,  privy,  or  manure  pile  at  a  higher  level  or  within  300 
feet  of  it. 

34.  The  dairy  building  shall  be  kept  clean  and  shall  not  be 
used  for  purposes  other  than  the  handling  and  storing  of  milk 
and  milk  utensils.     It  shall  be  provided  with  light  and  ventila- 
tion, and  the  floors  shall  be  graded  and  water-tight. 

35.  The  dairy  building  shall  be  well  lighted  and  screened, 
and  drained  through  well-trapped  pipes.     No  animals  shall  be 
allowed  therein.     No  part  of  the  dairy  building  shall  be  used 
for  dwelling  or  lodging  purposes,  and  the  bottling  room  shall  be 
used  for  no  other  purpose  than  to  provide  a  place  for  clean 
milk  utensils  and  for  handling  the  milk.     During  bottling  this 
room  shall  be  entered  only  by  persons  employed  therein.     The 


310        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

bottling  room  shall  be  kept  scrupulously  clean  and  free  from 
odors. 

36.  Temperature  of  Milk. — Proper  cooling  to  reduce  the 
temperature  to  45°  Ft  shall  be  used,  and  aerators  shall  be  so 
situated  that  they  can  be  protected  from  flies,  dust,  and  odors. 
The  milk  shall  be  cooled  immediately  after  being  milked,  and 
maintained  at  a  temperature  between  35°    and  45°   F.  until 
delivered  to  the  consumer. 

37.  Sealing  of  Bottles. — Milk,  after  being  cooled  and  bot- 
tled, shall  be  immediately  sealed  in  a  manner  satisfactory  to 
the   commission,   but   such   seal   shall   include    a    sterile   hood 
which  completely  covers  the  lip  of  the  bottle. 

38.  Cleaning  and  Sterilizing  of  Bottles. — The  dairy  building 
shall  be  provided  with  approved  apparatus  for  the  cleansing  and 
sterilizing  of  all  bottles  and  utensils  used  in  milk  production. 
All  bottles   and  utensils   shall  be  thoroughly  cleaned  by  hot 
water  and  sal  soda,  or  equally  pure  agent,  rinsed  until  the 
cleaning  water  is  thoroughly  removed,   then  exposed  to  live 
steam  or  boiling  water  at  least  twenty  minutes,  and  then  kept 
inverted  until  used,  in  a  place  free  from  dust  and  other  con- 
taminating materials. 

39.  Utensils. — All  utensils  shall  be  so  constructed  as  to  be 
easily  cleaned.     The  milk  pail  should  preferably  have  an  ellip- 
tical opening  five  by  seven  inches  in  diameter.     The  cover  of 
this  pail  should  be  so  convex  as  to  make  the  entire  interior  of  the 
pail  visible  and  accessible  for  cleaning.    The  pail  shall  be  made 
of  heavy  seamless  tin,  and  with  seams  which  are  flushed  and 
made  smooth  by  solder.     Wooden  pails,  galvanized-iron  pails, 
or  pails  made  of  rough,  porous  materials,  are  forbidden.     All 
utensils  used  in  milking  shall  be  kept  in  good  repair. 

40.  Water  Supply. — The  entire  water  supply  shall  be  abso- 
lutely free  from  contamination,  and  shall  be  sufficient  for  all 
dairy  purposes.     It  shall  be  protected  against  flood  or  surface 
drainage,  and  shall  be  conveniently  situated  in  relation  to  the 
milk  house. 

41.  Privies,  etc.,  in  Relation  to  Water  Supply. — Privies, 
pig-pens,  manure  piles,  and  all  other  possible  sources  of  con- 
tamination shall  be  so  situated  on  the  farm  as  to  render  im- 


APPENDIX  311 

possible  the  contamination  of  the  water  supply,  and  shall  be  so 
protected  by  use  of  screens  and  other  measures  as  to  prevent 
their  becoming  breeding  grounds  for  flies. 

42.  Toilet  Rooms. — Toilet  facilities  for  the  milkers  shall  be 
provided  and  located  outside  of  the  stable  or  milk  house.  These 
toilets  shall  be  properly  screened,  shall  be  kept  clean,  and  shall 
be  accessible  to  wash  basins,  water,  nail  brush,  soap,  and  towels, 
and  the  milkers  shall  be  required  to  wash  and  dry  their  hands 
immediately  after  leaving  the  toilet  room. 

TRANSPORTATION 

43,.  In  transit,  the  milk  packages  shall  be  kept  free  from  dust 
and  dirt.  The  wagon,  trays,  and  crates  shall  be  kept  scrupulously 
clean.  No  bottles  shall  be  collected  from  houses  in  which  com- 
municable diseases  prevail,  unless  a  separate  wagon  is  used  and 
under  conditions  prescribed  by  the  department  of  health  and  the 
medical  milk  commission. 

44.  All  certified  milk  shall  reach  the  consumer  within  thirty 
hours  after  milking. 

VETERINARY  SUPERVISION  OF  THE  HERD 

45.  Tuberculin  Test. — The  herd  shall  be  free  from  tubercu- 
losis, as  shown  by  the  proper  application  of  the  tuberculin  test. 
The  test  shall  be  applied  in  accordance  with  the  rules  and  regu- 
lations of  the  United  States  Government,  and  all  reactors  shall 
be  removed  immediately  from  the  farm.3 

46.  No  new  animals  shall  be  admitted  to  the  herd  without 
first  having  passed   a   satisfactory  tuberculin  test,  made  in 
accordance  with  the  rules  and  regulations  mentioned ;  the  tuber- 
culin to  be  obtained  and  applied  only  by  the  official  veterinarian 
of  the  commission. 

47.  Immediately  following  the  application  of  the  tuberculin 
test  to  a  herd  for  the  purpose  of  eliminating  tuberculous  cattle, 
the  cow  stable  and  exercising  yards  shall  be  disinfected  by  the 
veterinary  inspector  in  accordance  with  the  rules  and  regula- 
tions of  the  United  States  Government.3 

3  See  circular  of  Instructions  issued  by  the  Bureau  of  Animal 
Industry  for  making  tuberculin  tests  and  for  disinfection  of 
premises. 


312        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

48.  A  second  tuberculin  test  shall  follow  each  primary  test 
after  an  interval  of  six  months,  and  shall  be  applied  in  accord- 
ance with  the  rules  and  regulations  mentioned.     Thereafter, 
tuberculin  tests  shall  be  reapplied  annually,  but  it  is  recom- 
mended that  the  retests  be  applied  semi-annually. 

49.  Identification  of  Cows. — Each  dairy  cow  in  each  of  the 
certified  herds  shall  be  labeled  or  tagged  with  a  number  or  mark 
which  will  permanently  identify  her. 

50.  Herd-book  Record. — Each  cow  in  the  herd  shall  be 
registered  in  a  herd  book,  which  register  shall  be  accurately 
kept  so  that  her  entrance  and  departure  from  the  herd  and  her 
tuberculin  testing  can  be  identified. 

51.  A  copy  of  this  herd-book  record  shall  be  kept  in  the 
hands  of  the  veterinarian  of  the  medical  milk  commission  under 
which  the  dairy  farm  is  operating,  and  the  veterinarian  shall 
be  made  responsible  for  the  accuracy  of  this  record. 

52.  Dates  of  Tuberculin  Tests. — The  dates  of  the  annual 
tuberculin  tests  shall  be  definitely  arranged  by  the  medical  milk 
commission,  and  all  of  the  results  of  such  tests  shall  be  recorded 
by  the  veterinarian  and  regularly  reported  to  the  secretary  of 
the  medical  milk  commission  issuing  the  certificate. 

53.  The  results  of  all  tuberculin  tests  shall  be  kept  on  file  by 
each  medical  milk  commission,  and  a  copy  of  all  such  tests  shall 
be  made  available  to  the  American  Association  of  Medical  Milk 
Commissions  for  statistical  purposes. 

54.  The  proper  designated  officers  of  the  American  Associa- 
tion of  Medical  Milk   Commissions   should   receive   copies   of 
reports  of  all  of  the  annual,  semiannual,  and  other  official  tuber- 
culin tests  which  are  made,  and  keep  copies  of  the  same  on  file 
and  compile  them  annually  for  the  use  of  the  association. 

55.  Disposition  of  Cows  Sick  with  Diseases  Other  Than 
Tuberculosis. — Cows  having  rheumatism,  leucorrhaa,  inflamma- 
tion of  the  uterus,  severe  diarrhoea,  or  disease  of  the  udder,  or 
cows  that  from  any  other  cause  may  be  a  menace  to  the  herd, 
shall  be  removed  from  the  herd,  placed  in  a  building  separate 
from  that  which  may  be  used  for  the  isolation  of  cows  with 
tuberculosis,  unless  such  building  has  been  properly  disinfected 
since  it  was  last  used  for  this  purpose.    The  milk  from  such  cows 


APPENDIX  313 

shall  not  be  used,  nor  shall  the  cows  be  restored  to  the  herd  until 
permission  has  been  given  by  the  veterinary  inspector  after  a 
careful  physical  examination. 

56.  Notification  of  Veterinary  Inspector. — In  the  event  of 
the  occurrence  of  any  of  the  diseases  just  described  between  the 
visits  of  the  veterinary  inspector,  or  if  at  any  time  a  number  of 
cows  become  sick  at  one  time  in  such  a  way  as  to  suggest  the 
outbreak  of  a  contagious  disease  or  poisoning,  it  shall  be  the 
duty  of  the  dairyman  to  withdraw  such  sickened  cattle  from  the 
herd,  to  destroy  their  milk,  and  to  notify  the  veterinary  inspector 
by  telegraph  or  telephone  immediately. 

57.  Emaciated    Cows. — Cows    that    are    emaciated    from 
chronic  diseases  or  from  any  cause  that  in  the  opinion  of  the 
veterinary  inspector  may  endanger  the  quality  of  the  milk,  shall 
be  removed  from  the  herd. 

BACTERIOLOGICAL  STANDARDS 

58.  Bacterial  Counts. — Certified  milk  shall  contain  less  than 
10,000  bacteria  per  cubic  centimetre  when  delivered.     In  case  a 
count  exceeding  10,000  bacteria  per  cubic  centimetre  is  found, 
daily   counts   shall   be   made,   and  if  normal   counts   are  not 
restored  within  ten  days  the  certificate  shall  be  suspended. 

59.  Bacterial  counts  shall  be  made  at  least  once  a  week. 

60.  Collection  of  Samples. — The  samples  to  be  examined 
shall  be  obtained  from  milk  as  offered  for  sale,  and  shall  be 
taken  by  a  representative  of  the  milk  commission.    The  samples 
shall  be  received  in  the  original  packages,  in  properly  iced 
containers,  and  they  shall  be  so  kept  until  examined,  so  as  to 
limit  as  far  as  possible  changes  in  their  bacterial  content. 

61.  For  the  purpose  of  ascertaining  the  temperature,  a  sep- 
arate  original   package   shall   be   used,   and  the   temperature 
taken  at  the  time  of  collecting  the  sample,  using  for  the  purpose 
a  standardized  thermometer  graduated  in  the  centigrade  scale. 

62.  Interval  Between  Milking  and  Plating. — The  examina- 
tions shall  be  made  as  soon  after  collection  of  the  samples  as 
possible,  and  in  no  case  shall  the  interval  between  milking  and 
plating  the  samples  be  longer  than  forty  hours. 

63.  Plating. — The  packages  shall  be  opened  with  aseptic 


314        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

precautions  after  the  milk  has  been  thoroughly  mixed  by  vigor- 
ously reversing  and  shaking  the  container  twenty-five  times. 

64.  Two  plates  at  least  shall  be  made  for  each  sample  of 
milk,  and  there  shall  also  be  made  a  control  of  each  lot  of 
medium  and  apparatus  used  at  each  testing.     The  plates  shall 
be  grown  at  37°  C.  for  forty-eight  hours. 

65.  In  making  the  plates  there  shall  be  used  agaragar  media 
containing  1.5  per  cent,  agar  and  giving  a  reaction  of  1.0  to 
phenolphthalein. 

[The  method  recommended  by  a  committee  of  the  American 
Public  Health  Association  for  the  making  of  the  medium  is  to 
be  followed  (see  page  262),  modified,  however,  as  to  the  agar 
content  and  reaction  to  conform  to  the  requirements  specified 
in  section  65.] 

66.  Samples  of  milk  for  plating  shall  be  diluted  in  the  pro- 
portion of  1  part  of  milk  to  99  parts  of  sterile  water;  shake 
25  times  and  plate  1  c.c.  of  the  solution. 

[The  recommendations  of  the  committee  of  the  American 
Public  Health  Association  in  regard  to  plating  are  to  be  fol- 
lowed (see  page  265).] 

67.  Determination  of  Taste  and  Odor  of  Milk. — After  the 
plates  have  been  prepared  and  placed  in  the  incubator,  the 
taste  and  odor  of  the  milk  shall  be  determined  after  warming 
the  milk  to  100°  F.4 

68.  Counts. — The  total  number  of  colonies  on  each  plate 
should  be  counted,  and  the  results  expressed)  in  multiples  of  the 
dilution  factor.     Colonies  too  small  to  be  seen  with  the  naked 
eye  or  with  slight  magnification  shall  not  be  considered  in  the 
count. 

69.  Records  of  Bacteriologic  Tests. — The  results  of  all  bac- 
terial tests  shall  be  kept  on  file  by  the  secretary  of  each  commis- 
sion, copies  of  which  should  be  made  available  annually  for  the 
use  of  the  American  Association  of  Medical  Milk  Commissions. 

4  Should  it  be  deemed  desirable  and  necessary  to  conduct 
tests  for  sediment,  the  presence  of  special  bacteria,  or  the  num- 
ber of  leucocytes,  the  methods  adopted  by  the  committee  of  the 
American  Public  Health  Association  should  be  followed. 


APPENDIX  315 

CHEMICAL  STANDARDS  AND  METHODS 
The  methods  that  must  be  followed  in  carrying  out  the  chem- 
ical investigations  essential  to  the  protection  of  certified  milk 
are  so  complicated  that  in  order  to  keep  the  fees  of  the  chemist 
at  a  reasonable  figure  there  must  be  eliminated  from  the  exam- 
ination those  procedures  which,  whilst  they  might  be  helpful  and 
interesting,  are  in  no  sense  necessary. 

For  this  reason  the  determination  of  the  water,  the  total 
solids,  and  the  milk  sugar  is  not  required  as  a  part  of  the  routine 
examination. 

70.  The  chemical  analyses  shall  be  made  by  a  competent 
chemist  designated  by  the  medical  milk  commission. 

71.  Method  of  Obtaming  Samples. — The  samples  to  be  ex- 
amined by  the  chemist  shall  have  been  examined  previously  by 
the  bacteriologist  designated  by  the  medical  milk  commission 
as  to  temperature,  odor,  taste,  and  bacterial  content. 

72.  Fat  Standards. — The  fat  standard  for  certified  milk 
shall  be  4  per  cent.,  with  a  permissible  range  of  variation  of 
from  3.5  to  4.5  per  cent. 

73.  The  fat  standard  for  certified  cream  shall  be  not  less 
than  18  per  cent. 

74.  If  it  is  desired  to  sell  higher  fat-percentage  milks  or 
creams  as  certified  milks  or  creams,  the  range  of  variation  for 
such  milks  shall  be  0.5  per  cent,  on  either  side  of  the  advertised 
percentage  and  the  range  of  variations  for  such  creams  shall  be 
2  per  cent,  on  either  side  of  the  advertised  percentage. 

75.  The  fat  content  of  certified  milks  and  creams  shall  be 
determined  at  least  once  each  month. 

76.  The  methods  recommended  for  this  purpose   are  the 
Babcock   (a),  the  Leffmann-Beam   (&),  and  the  Gerber   (c). 
(See  pages  233  to  239.) 

77.  Before  condemning  samples  of  milk  which  have  fallen 
outside  the  limits  allowed,  the  chemist  shall  have  determined,  by 
control  ether  extractions,  that  his  apparatus  and  his  technic 
are  reliable. 

78.  Protein  Standard. — The  protein  standard  for  certified 
milk  shall  be  3.50  per  cent.,  with  a  permissible  range  of  varia- 
tion of  from  3  to  4  per  cent. 


316        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

79.  The  protein  standard  for  certified  cream  shall  corre- 
spond to  the  protein  standard  for  certified  milk. 

80.  The  protein  content  shall  be  determined  only  when  any 
special  consideration  seems  to  the  medical  milk  commission  to 
make  it  desirable. 

81.  It  shall  be  determined  by  the  Kjeldahl  method,  using 
the  Gunning  or  some  other  reliable  modification,  and  employing 
the  factor  6.25  in  reckoning  the  protein  from  the  nitrogen. 

KjeldaM  Method. — Five  cubic  centimetres  are  measured 
carefully  into  a  flat-bottom  800  c.c.  Jena  flask,  20  c.c.  of  concen- 
trated sulphuric  acid  (C.  P.;  sp.  gr.,  1.84)  are  added,  and  0.7 
gramme  of  mercuric  oxide  (or  its  equivalent  in  metallic  mer- 
cury) ;  the  mixture  is  then  heated  over  direct  flame  until  it  is 
straw-colored  or  perfectly  white;  a  few  crystals  of  potassium 
permanganate  are  now  added  till  the  color  of  the  liquid  remains 
green.  All  the  nitrogen  in  the  milk  has  then  been  converted 
into  the  form  of  ammonium  sulphate.  After  cooling,  200  c.c. 
of  ammonia-free  distilled  water  are  added,  20  c.c.  of  a  solution  of 
potassium  sulphide  (containing  40  grammes  sulphide  per  litre), 
and  a  fraction  of  a  gramme  of  powdered  zinc.  A  quantity  of 
semi-normal  HC1  solution  more  than  sufficient  to  neutralize  the 
ammonia  obtained  in  the  oxidation  of  the  milk  is  now  carefully 
measured  out  from  a  delicate  burette  (divided  into  1/20  c.c.) 
into  an  Erlenmeyer  flask  and  the  flask  connected  with  a  distil- 
lation apparatus.  At  the  other  end  the  Jena  flask  containing 
the  watery  solution  of  the  ammonium  sulphate  is  connected, 
after  adding  50  c.c.  of  a  concentrated  soda  solution  (1  pound 
"pure  potash"  dissolved  in  500  c.c.  of  distilled  water  and  allowed 
to  settle)  ;  the  contents  of  the  Jena  flask  are  now  heated  to 
boiling,  and  the  distillation  is  continued  for  40  minutes  to  an 
hour,  until  all  ammonia  has  been  distilled  over. 

The  excess  of  acid  in  the  Erlenmeyer  receiving  flask  is  then 
accurately  titrated  back  by  means  of  a  tenth-normal  standard 
ammonia  solution,  using  a  cochineal  solution  as  an  indicator. 
From  the  amount  of  acid  used  the  per  cent,  of  nitrogen  is  ob- 
tained; and  from  it  the  per  cent,  of  casein  and  albumen  in  the 
milk  by  multiplying  by  6.25.  The  amount  of  nitrogen  contained 
in  the  chemicals  used  is  determined  by  blank  experiments  and 


APPENDIX  317 

deducted  from  the  nitrogen  obtained  as  described.    (Farrington 
and  Woll,  Testing  Milk  and  Its  Products,  p.  221.) 

82.  Coloring  Matter  and  Preservatives. — All  certified  milks 
and  creams  shall  be  free  from  adulteration,  and  coloring  matter 
and  preservatives  shall  not  be  added  thereto. 

83.  Tests  for  the  detection  of  added  coloring  matter  shall  be 
applied  whenever  the  color  of  the  milk  or  cream  is  such  as  to 
arouse  suspicion. 

Test  for  Coloring  Matter. — The  presence  of  foreign  color- 
ing matter  in  milk  is  easily  shown  by  shaking  10  c.c.  of  the  milk 
with  an  equal  quantity  of  ether ;  on  standing,  a  clear  ether  solu- 
tion will  rise  to  the  surface ;  if  artificial  coloring  matter  has  been 
added  to  the  milk,  the  solution  will  be  yellow  colored,  the  inten- 
sity of  the  color  indicating  the  quantity  added;  natural  fresh 
milk  will  give  a  colorless  ether  solution.  (Testing  Milk  and  Its 
Products,  Farrington  and  Woll,  p.  244.) 

84.  Tests  for  the  detection  of  formaldehyde,  borax,  and 
boracic  acid  shall  be  applied  at  least  once  each  month.     Occa- 
sionally application  of  tests  for  the  detection  of  salicylic  acid, 
benzoic  acid,  and  the  benzoates  are  also  recommended.     (See 
pages  257  to  260.) 

85.  Detection  of  Heated  Milk. — Certified  milk  or  cream 
shall  not  be  subjected  to  heat  unless  specially  directed  by  the 
commission  to  meet  emergencies. 

86.  Tests  to  determine  whether  such  milks  and  creams  have 
been  subjected  to  heat  shall  be  applied  at  least  once  each  month. 
(See  page  298.) 

87.  Specific  Gravity. — The  specific  gravity  of  certified  milk 
shall  range  from  1.029  to  1.034. 

88.  The  specific  gravity  shall  be  determined  at  least  each 
month.  (See  page  228.) 

METHODS  AND  REGULATIONS  FOR  THE  MEDICAL  EXAMINA- 
TION OF  EMPLOYEES,  THEIR  HEALTH  AND 
PERSONAL  HYGIENE 

89.  A  medical  officer  known  as  the  attending  dairy  physi- 
cian shall  be  elected  by  the  commission,  who  should  reside  near 
the  dairy  producing  certified  milk.     He  shall  be  a  physician 
in  good  standing  and  authorized  by  law  to  practice  medicine; 


318        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

he  shall  be  responsible  to  the  commission  and  subject  to  its  direc- 
tion. In  case  more  than  one  dairy  is  under  the  control  of  the 
commission  and  they  are  in  different  localities,  a  separate 
physician  should  be  designated  for  employment  for  the  super- 
vision of  each  dairy. 

90.  Before  any  person  shall  come  on  the  premises  to  live 
and  remain  as  an  employee,  such  person,  before  being  engaged 
in  milking  or  the  handling  of  milk,  shall  be  subjected  to  a  com- 
plete physical  examination  by  the  attending  physician.    No  per- 
son shall  be  employed  who  has  not  been  vaccinated  recently  or 
who  upon  examination  is  found  to  have  a  sore  throat,  or  to 
be  suffering  from  any  form  of  tuberculosis,  venereal  disease, 
conjunctivitis,    diarrhoea,    dysentery,    or    who  has     recently 
had  typhoid  fever  or  is  proved  to  be  a  typhoid  carrier,  or  who 
has  any  inflammatory  disease  of  the  respiratory  tract,  or  any 
suppurative  process  or  infectious  skin  eruption,  or  any  disease 
of  an  infectious  or  contagious  nature,  or  who  has  recently  been 
associated  with  children  sick  with  contagious  disease. 

91.  In  addition  to  ordinary  habits  of  personal  cleanliness,  all 
milkers  shall  have  well-trimmed  hair,  wear  close-fitting  caps,  and 
have  clean-shaven  faces. 

92.  When  the  milkers  live  upon  the  premises  their  dormi- 
tories shall  be  constructed  and  operated  according  to  plans 
approved  by  the  commission.    A  separate  bed  shall  be  provided 
for  each  milker,  and  each  bed  shall  be  kept  supplied  with  clean 
bedclothes.     Proper  bathing  facilities  shall  be  provided  for  all 
employees  on  the  dairy  premises,  preferably  a  shower  bath, 
and  frequent  bathing  shall  be  enjoined. 

93.  In  case  the  employees  live  on  the  dairy  premises,  a 
suitable  building  shall  be  provided  to  be  used  for  the  isolation 
and  quarantine  of  persons  under  suspicion  of  having  a  con- 
tagious disease. 

The  following  plan  of  construction  is  recommended : 

The  quarantine  building  and  hospital  should  be  one  story 

high  and  contain  at  least  two  rooms,  each  with  a  capacity 

of  about  6000  cubic  feet  and  containing  not  more  than  three 

beds  each,  the  rooms  to  be  separated  by  a  closed  partition.    The 


APPENDIX  319 

doors  opening  into  the  rooms  should  be  on  opposite  sides  of 
the  building,  and  provided  with  locks.  The  windows  should  be 
barred  and  the  sash  should  be  at  least  five  feet  from  the  ground, 
and  constructed  for  proper  ventilation.  The  walls  should  be 
of  a  material  which  will  allow  proper  disinfection.  The  floor 
should  be  of  painted  or  washable  wood,  preferably  of  concrete, 
and  so  constructed  that  the  floor  may  be  flushed  and  properly 
disinfected.  Proper  heating,  lighting,  and  ventilating  facili- 
ties should  be  provided. 

94.  In  the  event  of  any  illness  of  a  suspicious  nature,  the 
attending  physician  shall  immediately  quarantine  the  suspect, 
notify  the  health  authorities  and  the  secretary  of  the  commis- 
sion, and  examine  each  member  of  the  dairy  force ;  and  in  every 
inflammatory  affection  of  the  nose  or  throat  occurring  among 
the  employees  of  the  dairy,  in  addition  to  carrying  out  the 
above-mentioned  program,  the  attending  physician  shall  take 
a  culture  and  have  it  examined  at  once  by  a  competent  bacteri- 
ologist approved  by  the  commission.    Pending  such  examination, 
the  affected  employee  or  employees  shall  be  quarantined. 

95.  It  shall  be  the  duty  of  the  secretary,  on  receiving  notice 
of  any  suspicious  or  contagious  disease  at  the  dairy,  at  once  to 
notify  the  committee  having  in  charge  the  medical  supervision 
of  employees  of  the  dairy  farm  upon  which  such  disease  has 
developed.    On  receipt  of  the  notice,  this  committee  shall  assume 
charge  of  the  matter  and  shall  have  power  to  act  for  the  com- 
mission as  its  judgment  dictates.    As  soon  as  possible  thereafter, 
the  committee  shall  notify  the  commission,  through  its  secretary, 
that  a  special  meeting  may  be  called  for  ultimate  consideration 
and  action. 

96.  When  a  case  of  contagious  disease  is  found  among  the 
employees  of  a  dairy  producing  certified  milk  under  the  control 
of  a  medical  milk  commission,  such  employee  shall  be  at  once 
quarantined  and  as  soon  as  -possible  removed  from  the  plant,  and 
the  premises  fumigated. 

When  a  case  of  contagion  is  found  on  a  certified  dairy  it 
is  advised  that  a  printed  notice  of  the  facts  shall  be  sent  to 
every  householder  using  the  milk,  giving  in  detail  the  precautions 
taken  by  the  dairyman  under  the  direction  of  the  commission, 


320        PRINCIPLES  AND  PRACTICE  OF  MILK  HYGIENE 

and  it  is  further  advised  that  all  milk  produced  at  such  dairy 
shall  be  heated  at  145°  F.  for  40  minutes,  or  155°  F.  for  30 
minutes,  or  167°  F.  for  20  minutes,  and  immediately  cooled  to 
50°  F.  These  facts  should  also  be  part  of  the  notice,  and  such 
heating  of  the  milk  should  be  continued  during  the  accepted 
period  of  incubation  for  such  contagious  disease. 

The  following  method  of  fumigation  is  recommended : 

After  all  windows  and  doors  are  closed  and  the  cracks  sealed 
by  strips  of  paper  applied  with  flour  paste,  and  the  various 
articles  in  the  room  so  hung  or  placed  as  to  be  exposed  on  all 
sides,  preparations  should  be  made  to  generate  formaldehyde 
gas  by  the  use  of  20  ounces  of  formaldehyde  and  10  ounces  of 
permanganate  of  potash  for  every  1000  cubic  feet  of  space  to 
be  disinfected. 

For  mixing  the  formaldehyde  and  potassium  permanganate 
a  large  galvanized-iron  pail  or  cylinder  holding  at  least  20 
quarts  and  having  a  flared  top  should  be  used  for  mixing  therein 
20  ounces  of  formaldehyde  and  10  ounces  of  permanganate.  A 
cylinder  at  least  5  feet  high  is  suggested.  The  containers 
should  be  placed  about  in  the  rooms  and  the  necessary  quantity 
of  permanganate  weighed  and  placed  in  them.  The  formalde- 
hyde solution  for  each  pail  should  then  be  measured  into  a 
wide-mouthed  cup  and  placed  by  the  pail  in  which  it  is  to  be 
used. 

Although  the  reaction  takes  place  quickly,  by  making  prep- 
arations as  advised  all  of  the  pails  can  be  "  set  off  "  promptly 
by  one  person,  since  there  is  nothing  to  do  but  pour  the  formalde- 
hyde solution  over  the  permanganate.  The  rooms  should  be 
kept  closed  for  four  hours.  As  there  is  a  slight  danger  of  fire, 
the  reaction  should  be  watched  through  a  window  or  the  pails 
placed  on  a  noninflammable  surface. 

97.  Following  a  weekly  medical  inspection  of  the  employees, 
a  monthly  report  shall  be  submitted  to  the  secretary  of  the 
medical  milk  commission,  on  the  same  recurring  date  by  the 
examining  visiting  physician. 

The  following  schedule,  filled  out  in  writing  and  signed  by 
himself,  is  recommended  as  a  suitable  form  for  the  attending 
physician's  report: 


APPENDIX  321 

This  is  to  certify  that,  on  the  dates  below  indicated,  official 

visits  were  made  to  the dairy,  owned  and  conducted  by 

of (indicating  town  and  state),  where  careful 

inspections  of  the  dairy  employees  were  made. 

(a)   Number  and  dates  of  visits  since  last  report.  >. 

(&)   Number  of  men  employed  on  the  plant.  . 

(c)  Has  a  recent  epidemic  of  contagion  occurred  near  the 
dairy,  and  what  was  its  nature  and  extent?    . 

(d)  Have   any   cases    of   contagious    or   infectious   disease 
occurred  among  the  men  since  the  last  report? . 

(e)  Disposition  of  such  cases.  . 

(/)   What  individual  sickness  has  occurred  among  the  men 

since  the  last  report?  . 

(g)  Disposition  of  such  cases. . 

(h)  Number  of  employees   now  quarantined!  for   sickness. 


(i)  Describe  the  personal  hygiene  of  the  men  employed  for 
milking  when  prepared  for  and  during  the  process  of  milking. 

0)    What  facilities  are  provided  for  sickness  in  employees? 

(Ar)  General  hygienic  condition  of  the  dormitories  or  houses 
of  the  employees.  . 

(I)    Suggestions  for  improvement.  . 

(m)  What  is  the  hygienic  condition  of  the  employees  and 
their  surroundings?  . 

(n)  How  many  employees  were  examined  at  each  of  the 
foregoing  visits?  . 

(o)   Remarks. 


Attending  Physician. 
Date, . 


INDEX 


Abortion,  infectious,   116 
Acid-forming  bacteria,  51 
Acidity,  determination  of,  254 
Acidity    test   with   Babcock 

pipette,  256 
Actinomycosis,  102 
Adulteration,  detection  of,  24$ 
Adulteration,   determination   of 

degree  of,  246 
Aerator,  182 
Age  of  milk,  64 
Aggressins,  45 
Alcohol  test,  285 
Alkalies,  test  for,  260 
Anaerobic  bacteria,  57 
Animal-like  taste,  28 
Anthrax,  100 
Antibodies,  42 
Antiformin  method,  277 
Aphthous  fever,  96 
Arnold's  guaiac  test,  29 8 

Babcock  test,  233 
Bacillus  abortus   116,   117 

aero  genes,  56 

bulgaricus,  54,  55 

coli,  56 

Guillebeau,  54 

lactis  aerogenes,  53,  56 

lactimorbi,  104 

mesentericus  vulgatus,  60 

proteus  vulgaris,  61 

pyogenes,  108 

subtilis,    60 

typhosus,  121 


Bacteria,   acid-forming,   51 

alkali-forming,  6l 

anaerobic,    57 

common-milk,  effect  of  heat 
on,   209 

counting,  260 

gas-forming,  55 

inert,    61 

of  milk,  50 

pathogenic,    effect    of    heat 
on,  204 

peptonizing,    58 

proportion   of   different 
groups,  64 

variations    in    number    and 

kind,  62 

Bactericidal  action  of  milk,   43 
Bacterium  acidi  lactici,   53,   54, 
55,  56 

lactis  acidi,  52 
Bedding,  178 

Benzoic  acid,  test  for,  259 
Beet-like  taste,  71 
Biorization,   222 
Bitter  milk,  69 
Bitter  taste,  28,  29,  30 
Black  scab,  100 
Blood  in  milk,  113 
Blue   milk,   71 
Borax,  tests  for,  257 
Boiling  test,  284 
Boric  acid,  tests  for,  257 
Burnt  taste,  30 
Burnt  taste  and  odor,  71 
Butyric  acid  bacteria,  57 
323 


324 


INDEX 


Calculation  of  total   solids,  241 
Casease   bacteria,    58 
Casein,    1 4 
Catalase,  38 
Catalase  test,  287 
Catarrhal   mastitis,    105 
Cells,  number  of  in  milk,  34 
Cellular  content  of  milk,  34 
Certified1  milk,  46 

methods  and  standards,  303 
Clarification,   175 
Clarifier,   175 
Cleaning  milk  vessels,  189 

the  cows,  166 

the  stable,  method  of,  160 
Cocci,  udder  59 
Coli-aerogenes  bacteria,  55,  56 
Coli,  examination  for,  275 
Color,  examination  of,  227 
Color,  of  milk,  28 
Coloring  matters,  examination 

for,  301 
Colostrum,  bactericidal  power,  13 

change  of  to  milk,  13 

chemical  properties,    11 

ferments  or  enzymes,  12 

judgment   of   as   food   for 
man,  13 

microscopic  appearance,  12 

reaction,  12 

physical   properties,    1 1 
Common  milk  bacteria,  50 
Composition  of  milk,  variations, 

19 

Consistency,  examination  of,  227 
Cooked  taste,  30 
Coolers,  types   of,   182 
Coolers,    conical,    183 

corrugated,  183 

double-tube,  186 

internal,  186 


Coolers,  regenerative,  219 

tubular,    184 
Counting  bacteria,  collection  of 

samples,   260 
microscopic  method,  267 
plate  method,  262 
Covered-top   pail,   172 
Cows,    examination    for    cleanli- 
ness, 148 

for    symptoms    of    dis- 
ease, 150 
Cow  fly,  164 
Cow-like  taste,  66 
Cowpox,  97 

false,  99 

Cows,  stage  of  lactation,   149 
Cream   layer,    17 
line,  17 

line,  effect  of  heat  on,  213 
Cubic  air  space,  136 
Curdling,   premature,  68 
sour,   1 5 
sweet,   15 

Dairy  Farm  Inspection,  126 
Decomposition    products,     effect 

of  heat  on,  210 
Diastase,  37 

test,  297 
Dilution,    effect   of   on   infected 

milk,  73 
influence  of  on  tuberculous 

infection,  86 
Diphtheria,  123 

bacilli,   effects   of   heat   on, 

205 

Direct   infection,    72 
Dirt,  examination  for,  299 
Disease,  influence  of  on  milk,  72 


INDEX 


325 


Diseases    of    cattle   which   may 
render  milk  harmful,  104 
of    cattle    transmissible 

through   milk,   72 
of  man  transmissible  through 

milk,    119 

Doane-Buckley  Method,  282 
"  Dry  "  cows,  3 
matter,  19 

Electricity,  222 

Electrical  conductivity  of  milk, 

34 
Enteritis,  septic  or  hemorrhagic, 

114 

Enzymes,  12,  36 
bacterial,  37 
original  37 
effect  of  heat  on,  213 
Examining  milk,  methods  of ,  223 
Excretion  of  medicines  through 
udder,  119 

Failure  to  Sour  and  "  Butter/'  70 

False  cowpox,  99 

Farrington's  alkaline  tablet  test, 

256 
Fat,   16 

per  cent.,  determination  of, 
233 

per  cent,  in  total  solids,  de- 
termination of,  246 
Feed  boils,  100 
Feeding,  175 
Ferments,  bacterial,  37 

effect  of  heat  on,  213 

original,  37 

Fermentation-reductase  test,  296 
Fermentation  test,  278 
"Fishy"  milk,  67 

taste,  29 


"Flaky"  milk,  107,  109 
Fleshy  udder,  3 
Flies,  161 

cow  fly,   164 

horn  fly,  164 

house  fly,   162 

stable  fly,  165 

Formaldehyde,  tests  for,  258 
Foot  and  mouth  disease,  96 
Foul  and  unpleasant  odor  and 

taste,   29 

Freezing   point  of  milk,   33 
"  Fresh  "  cows,  4 
Fritzmann's  Method,  248 
Furunculosis  of  the  udder,  99 

Gas-forming  bacteria,  55 
Gerber  test,   237 
Germicidal  action  of  milk,   43 
Gravimetric   method    for    deter- 
mination of  total  solids,  240 
Greenish-yellow  spots,   71 
"  Gritty  "  milk,  68 

Hay  bacillus,  60 
Heated  milk,  tests  for,  298 
Holder    and    pasteurizer    com- 
bined, 220 
Holding   tank,    219 
Homogenized  milk,  17 
Horn  fly,  164 
House  fly,   162 

Ice,   quantity   required,    187 
Indigestion,   114 
Inert  bacteria,  61 
Infection,  direct,  72 

secondary,  72 

Inflammation  of  the  udder,  104 
Influence  of  disease  on  milk,  72 
Immune  bodies,  42 


326 


INDEX 


Inspection  of  dairy  farms,  126 
Interstitial  mastitis,   109 
Intestinal  tuberculosis,  diagnosis 

of,  95 
Involution,  2 

Lactalbumin,  16 
Lactation,  physiology  of,  1 

stages  of,  3 
Lactoglobulin,  16 
Lactometer,  Quevenne's,  228 
Lactose,  18 

test  for,  301 
Lactoscope  test,  239 
Leach's    test,    259 
Legal  standards,  23,  24,  25 
Leucocytes,   estimation  of  num- 
ber,  281 

"  Letting  down,"  7 
Litmus  test,  254 

Malt-like  taste  and  odor,  71 
Manure-like  odor,  30 
Mann's  acidity  test,  254 
Market  milk,   classes  or   grades 

of,   45 

composition    of,    22 
frequency    of   tubercle    ba- 
cilli  in,   73 
prevention  of  contamination 

with  tubercle  bacilli,  90 
Mastitis,  104 

catarrhal,   105 

interstitial,    109 

milk,  harmful  properties  of, 

110 

parenchymatous,  108 

tuberculous,    81,   93 

Medicines,   excretion   through 

udder,   119 
Metritis,   septic,    115 


Milk,  opacity  of,   18 

biological  properties,  36 

cellular  content,  34 

chemical  properties,  14 

color,  28 

defects,  66 

electrical  conductivity,  34 

ferments  or  enzymes,  36 

freezing  point,  33 

odor   and   taste   of,   28 

pails,  types   of,  172 

physical  properties,  28 

reaction,  26 

refraction,  32 

secretion,   phases   of,   6 
first  phase,  6 
second  phase,  7 

sickness,  104 

solids,    19 

specific  gravity  of,  30 

surface  tension,  33 
Milk  house,  apparatus,  182 

construction,  181 

location,  180 

water  supply,  193 
Milk  vessels,  methods  of  clean- 
ing, 183 
sterilization  of,  190 

viscosity,  33 
Milking   machines,    methods    of 

cleaning,  192 
Milking,  methods  of,   168 

Nauseating  taste,  30 

Nitrates  and  nitrites,  tests  for, 

247 
Nutritive    properties,    effect    of 

heat  on,  211 

Odor,  examination  of,  227 
0dor  and  taste  of  milk,  28 


INDEX 


327 


Odors,  absorption  of  by  milk,  29 

(Edema  of  the  udder,  113 

Oily   taste,    30 

Opacity  of   milk,   18 

Open  Tuberculosis,  diagnosis  of, 

94 

Orange-colored  spots,  71 
Original  contamination,  63 
Ozone,   222 

Paratyphoid  fever,   123 

Parenchymatous  mastitis,  108 

Pasteurization,  203 

"  flash"  process,  214 
continuous   process,   214 
"holder"  process,  214 
in  final  container,  214 
methods  of,  214 
principles  of,  204 
summary  of  effects  of,  213 

Pasteurizers,  types  of,  215 

Peptonizing  bacteria,  58 

Peroxydase,   38 

Peter's    test,    259 

Physiology  of  milk  secretion,  1 

Potato  bacillus,  60 

Premature   curdling,    68 

Preservatives,  tests  for,  257 

Rabies,  101 
Rancid  milk,  67 

odor  and'  taste,  30 

taste,  28 
Reaction,  determination  of,  254 

of  colostrum,   12 

of  milk,  26 
Red  milk,  71 
Reductase,  39 

test,   294 


Refractive  index,  32 
Refraction    number,    determina- 
tion of,  250 

Regenerative  cooler,  219 
Remont's  test,  259 
Retained  placenta,  116 
Retarder,  220 
Richmond's  test,  258 
"  Ropy  "  milk,   69 
Rosolic  acid  test,  260 

Salicylic  acid,  test  for,  259 

Salts,  19 

Salty,  cow-like  taste,  66 

taste,  28 
Samples,  collecting,  223 

individual,  226 

mixing,  226 

preserving,  224 

stable  or  herd,  225 
"Sandy"  milk,  68 
Scarlet  fever,  125 
Score  cards,  197 
Secondary   infection,    72 
Secretion  of  milk,  first  phase,  6 
phases  of,  6 
physiology,  1 
second  phase,  7 
Septic  sore  throat,  124 
Slow-creaming  milk,  67 
"  Soapy  "  taste,  70 
Solid's,  determination  of,  240 

by  automatic  reckoner,  245 

by  calculation,  241 

Gravimetric  method,  240 

determination    of   specific 

gravity  of,  246 
Solids  not  fat,  19 

determination  of,  245 
Sore  throat,  septic,  124 


328 


INDEX 


Sour  curdling,   15 

odor  and  taste,  30 
Soxhlet's  test,  247 
Specific  gravity,  determination 

of,  228 
of  milk,  30 

of   milk    solids,    deter- 
mination of,  246 
Spoiled  feed,  effects  of  on  milk, 

114 
Stable,  ceiling,  139 

drop,    144 

exposure,  129 

exterior,  129 

feed  trough,  143 

floor  of  stall,  144 

gutter,  144 

interior  construction,  139 

light,  146 

location,   1 29 

manger,    143 

odor  of  air,   131 

platform,   140 

ties,    145 

type,  129 

walls,  139 

stall  divisions,  145 

stanchions,  145 

surroundings,    1 30 
Stable  fly,  165 
Stable-like  odor  and  taste,  29,  30 

taste,  71 
Stable  practices,  159 

bedding,   178 

cleaning  the  cows,  166 

cleaning  the  stable,  160 

feeding,  175 

milking,   168 

time  required,    179 
Stages  of  lactation,  3 


Stalls,  arrangement  of,   145 

hospital  and  maternity,  146 

Standards,   legal,   for   milk   and 
cream,  23,  24,  25 

Staphylococcus  pyogenes,  59 

Sterilization  of  milk  vessels,  190 

Stewart's  test,  281 

Stokes'  test,  281 

Storch's  test,  298 

Strainers,    1 73 

Streptococci,    examination    for, 

272 
of  mastitis,  53 

Streptococcus  lacticus,  52,  54,  55 
pyogenes,"  effect  of  heat  on, 
205 

Stringy  milk,   69 

"  Strippers,"  5 

Structure  of  udder,  1 

Surface  tension  of  milk,  33 

Sweet  curdling,  15 

Taste,  effect  of  heat  on,  213 
examination  of,  227 
and  odor  of  milk,  28 
Temperature,    effect    on    growth 

of  bacteria,  63 
Total  solids,  19 

determination  of,  240 
Toxins,  44 
Trembles,  104 
Trommsdorff  test,  282 
Tubercle  bacilli, 

from    cattle,    virulence 

of,  for  man,  75 
conditions  under  which 
milk  is  infected  with, 
81 

effect  of  heat  on,  205 
examination  for,  275 


INDEX 


329 


Tubercle  bacilli,  frequency  of  in 

market  milk,  73 
human   type,    in    milk, 

125 
influence  of  dilution  on, 

86 

prevention  of  contami- 
nation of  market  milk 
with,  90 

Tuberculosis,  intestinal,  diagno- 
sis of,  95 

open,  diagnosis  of,  94 
of  the  udder,  diagnosis  of, 

94 

uterine,  diagnosis   of,  95 
Turmeric  test,  258 
Turnip-like   taste,    71 
Typhoid  fever,  121 

bacilli,  effects   of  heat 

on,  205 
Toxins,  effect  of  heat  on,  210 

Unclean   taste,   SO 
Udder  cocci,  59 

diagnosis  of  tuberculosis  of, 
94 

fleshy,  3 


Udder,  inflammation  of,  104 

oedema  of,   113 

structure  of,  1 
Ultra-violet    rays,    222 
Uterus,  diagnosis  of  tuberculosis 
of,  95 

Variations   in   composition   of 
milk,   19 

causes  of,  20 
Ventilation,  132 

cloth  method,  135 

King  system,  132 
Villier's  and  Fayolles'  test,  257 
Virulence    of    tubercle     bacilli 

from  cattle  for  man,  75 
Viscid  milk,  69 
Viscosity  of  milk,  33 
Violet-colored  spots,  71 

Water,  19 

supply,  193 
Westphal  balance,  229 

Yellow  spots,  71 
Yellowish-green  milk,  71 
Yellowish-green  spots,  71 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

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WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


OCT  12     1944 


LD  21-100m-12,  '43  (8796s) 


C   !>  1 

J 


YC  20703 


.y.-,.S..aE.RKELEY  LIBRARIES 


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